There is no requisite for salvation associated with the Trinity, the only true requirement is believing on and accepting the Messiah. In christianity this is Jesus who is the only Son of God the Father.
The sacrifice for salvation of man required by God was blood. In this case, the blood of an innocent, which was Jesus.
This arrangement between God and Jesus, went all the way back to the time of Adam. Prior to the time of Christ, starting with Adam, was the belief in the promise and coming of the Messiah and the sacrifice of a lamb for sins. The promise was first given by God to Adam and Eve in the Garden moments before their exile.
Salvation during this period in history, time periods also being referred to dispensations, require the belief on the coming of the Messiah and giving blood sacrifices until the promise of the Messiah was fulfilled.
The first recorded experience of this kind was Cain and Abel, brothers and sons of Adam and Eve. With the blood of Jesus being shed, salvation now runs through Him as the Christ (Genesis 4:3-10; 1 Thess. 5:9-10; Romans 10:13; 9-10; 1 John 5:11-14; Ephesians 1:20-21; 6:12; Matthew 28:18, Colossians 1:18-9, John 3:16-18, 36; Acts 4:12,).
Genesis 3:15 - First Promise of the Messiah
15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
The first account of the sacrifice was God Himself killing a lamb and clothing Adam and Eve in the Garden after their sin.
Genesis 3:21 - God performs first sacrifice himself to clothe Adam and Eve
21 Unto Adam also and to his wife did the Lord God make coats of skins, and clothed them.
The first account of the sacrifice by mans hands in recorded between Cain and Able which precipitated the first murder.
Genesis 4: 4–8 - The distinctions of what type of sacrifice was required
4 And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the Lord.
2 And she again bare his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground.
3 And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the Lord.
4 And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the Lord had respect unto Abel and to his offering:
5 But unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell.
6 And the Lord said unto Cain, Why art thou wroth? and why is thy countenance fallen?
7 If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him.
8 And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
Every person who died prior to Christ, died in faith believing on the coming of the Messiah. They had to receive Jesus AS the Messiah once He went into Paradise to minister to them for 3 days after His crucifixion.
13 These all died in faith, not having received the promises, but having seen them afar off, and were persuaded of them, and embraced them, and confessed that they were strangers and pilgrims on the earth.
Once they accepted Jesus as their savior, they rose out of Paradise and walked the earth again, waiting on their ascension to Heaven. This happened as a testimony to the resurrection of Christ.
50 Jesus, when he had cried again with a loud voice, yielded up the ghost.
51 And, behold, the veil of the temple was rent in twain from the top to the bottom; and the earth did quake, and the rocks rent;
52 And the graves were opened; and many bodies of the saints which slept arose,
53 And came out of the graves after his resurrection, and went into the holy city, and appeared unto many.
There is no biblical account that requires belief in the Trinity for Salvation regardless of when you lived in history.
9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
10 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
What became popular among Christians around the fourth century was that of a trinity of gods. It was not, however, a new idea conceived by Christians, there is much evidence of widespread belief in similar ideas throughout earlier recorded history.
Many scholars believe that the Trinity, as taught by Christians, comes from Plato as suggested in the Timaeus, but the Platonic trinity is itself merely a rearrangement of older trinities dating back to earlier peoples.
In Indian religion there is the Trinitarian group of Brahma, Vishna, and Shiva; in Egyptian religion there is the group of Kneph, Phthas, and Osiris. In Phoenicia the trinity of gods were Ulomus, Ulosuros, and Eliun. In Greece they were Zeus, Poseidon, and Aidoneus.
In Rome they were Jupiter, Neptune, and Pluto. In Babylonia and Assyria they were Anos, lllinos, and Aos. Among Celtic nations they were called Kriosan, Biosena, and Siva, and in Germanic nations they were called Thor, Wodan, and Fricco.
Trinities of gods existed in other cultures as well, including, but not limited to, those of Siberia, Persia, Japan, Scandinavia, and Mexico.
Although the Trinity is characteristic of the Christian religion, it is by no means peculiar to it. This has nothing to do with the veracity of the existence of the Trinity of God the Father, Son and Holy Spirit. This is a separate issue, the question of belief in the Trinity as a requisite to salvation is not required in any aspect of biblical history.