Does one have to seek forgiveness for past transgressions or is it forgiven through the realisation and the subsequent efforts?
I'm mildly confused by your question... are you asking if one must go about righting one's past offenses once one has come to realize them? Well that would be terrific, wouldn't it? Sure to gain extra-lovely strippers and extra tasty beer!
If one were to at least acknowledge one's previous mistakes and right one's course from there, that would at least be better than most wrong-doers have managed.
Are you asking if, for instance, one did something that hurt another and one ought to apologize? Certainly! Whether to forgive is always up to the other person. To apologize and amend is within the power of the offender. To accept is at the discretion of the offended.