God absolutely knows when in your heart you truly repent for your sins, and most importantly when you truly believe Jesus died for your sins and rose from death afterwards and your faith is truly in Him and His grace and no other way.  He then supernaturally sends The Holy Spirit to live in you.   

A modern description would be that God Himself celebrates and authenticates the moment by sending His Spirit into you Himself when he knows the change of mind and gives you a new heart Himself.  

God knows when in your heart you truly repent for your sins, and most importantly when you truly believe Jesus died for your sins and rose from death afterwards and your faith is truly in Him and His grace.  

A modern description would be that God Himself celebrates and authenticates the moment by sending His Spirit into you Himself when he knows the change of mind and gives you a new heart Himself.  

We encourage you to watch and listen to a preacher explain this topic. Marvel Not Ye Must Be Born Again.

The bible says of Jesus : 

[John 1:10-13 KJV] "He was in the world, and the world was made by him, and the world knew him not. He came unto his own, and his own received him not. But as many as received him, to them gave he power to become the sons of God, [even] to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God."

Jesus said : 

Jhn 3:3 KJV] Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.

[Jhn 3:6 KJV] That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.

[Jhn 3:7 KJV] Marvel not that I said unto thee, Ye must be born again.[

[1Pe 1:23 KJV] Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.

Just like being 'Baptized by the Holy Ghost', being 'Born Again' is another miraculous and everlasting act of God that He performs inside a brand new believer who has accepted Jesus through sincere faith.

Because it is a miracle and it gives life, only God can do it.  It's a gift from God who is the only one that can know a person's true heart and mind when it comes to matters of faith.  

When God sends His Holy spirit to live in our bodies He gives us a new spirit.  We have a soul, but we are spiritually dead insdie.  We all have an antichrist spirits residing in us, until we accept Christ is the Way, The Life & The Truth where we are given a new spirit and a new life that seeks the things of God and lives for the things of God.  

Before this happens we offer to lay down our life of sin willingly, believe on Jesus and the Gospel and ask God and Jesus into our life and ask for Him to help us.  

If God has not performed a miracle in you,  meaning put His Spirit into you - and given you a new spiritual life inside and made all things new to you  - or if you're not sure - you've likely not been born again.  

Maybe you've felt the presence of the Holy Ghost convincing you of your sin, and maybe you've pushed Him away.

If so...maybe you realized hearing the words of God,  or reading them you've felt convicted of your sin.  You've almost believed, but ultimately had doubts - or worried about what you would lose and not realizing what you will gain.  

Water baptism really is an outward expression of what shoud have been an inward condition.  Getting wet profits a man nothing.  Many people get dunked into water a dry sinner and come up a wet sinner.  

But Jesus Christ commands us to believe & be born again and baptized by His Spirit through belief in the name of Jesus.  

[2Co 5:17 KJV] Therefore if any man [be] in Christ, [he is] a new creature: old things are passed away; behold, all things are become new.

[Gal 6:15 KJV] For in Christ Jesus neither circumcision availeth any thing, nor uncircumcision, but a new creature.

[1Co 12:4 KJV] Now there are diversities of gifts, but the same Spirit.

[1Co 12:5 KJV] And there are differences of administrations, but the same Lord.

[1Co 12:6 KJV] And there are diversities of operations, but it is the same God which worketh all in all.

[1Co 12:12 KJV] For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also [is] Christ.

[1Co 12:13 KJV] For by one Spirit are we all baptized into one body, whether [we be] Jews or Gentiles, whether [we be] bond or free; and have been all made to drink into one Spirit.

[1Co 12:14 KJV]  For the body is not one member, but many.