"CHANGE YOUR MIND!"
Repent means "change of mind", according to Strong's NT Concordance rendering of the Greek word metanoea.
In this case it is a change of mind about one's own self in relationship to God.
It's about unbelievers realising their separation from Him by the Holy Spirit convicting them of sin.
Jesus said that the Spirit will ...
“... convict the world of sin ... because they do not believe in Me," John 16'7-11.
It is about mindset or worldview. Repenting is the act of a change mind about a worldview and the intention to take up a new mindset: the way of Christ.
The evidence of that change is a desire to live according to the new-found heavenly Father's will.
Like Paul who asked, “Lord, what do You want me to do?,” Acts 9'6.