I have done something wrong. What can I do about it? Apologise to someone if possible and appropriate. What else?
Apologise to God? No. He doesn't exist and, if he did, he would be responsible.
Confess to a priest or find salvation in Christ? No.
Think about it? Necessary but insufficient.
Avoid past mistakes? Yes but this is easier said than done and doesn't resolve guilt.
Say that the past doesn't matter? I think it does. See that there is a level on which the past doesn't matter? Maybe, but I am not at that level of perception yet.
Meditate? Yes, but that doesn't resolve the issue immediately. What will it be like to resolve it? Past actions either will not recur to memory or will somehow be perceived differently. Zazen moves us towards that different perception but on an uncontrollable time scale. Since the process cannot be hurried, in fact since it requires and involves patience, I cannot think of anything else to be done.