Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
33. It is a positive commandment for a sinner to turn from his sin and confess his sins in front of G-d.
As it says in Bamidbar (Numbers) 5:6-7, "A man or a woman [that has sinned]... and they shall confess in front of G-d." This confession should be with words in front of G-d. He should say the following from the depths of his heart: Please G-d, I have sinned, done wrong, and transgressed before you such and such sin is what I did (and he should name the sin). And I have regretted my sin and I am embarrassed by my deeds. Forever, I shall not return to doing this thing.
The main thing is remorse in the heart, and in truth, over the past, a person should take upon himself that he will not do the sin ever again. This is the main part of repentance. Anyone that does more confessions is praiseworthy. Even death and confession of Yom Kippur cannot atone for a person unless they have repented.
This is obligated in all places and at all times, for men and for women.