Forgiveness is not putting up with injustice. The truest test of forgiveness is when you do everything you possibly can to fight injustice in non-violent ways, and still manage to forgive the unjust even as you fight them.
Forgiveness has to be ongoing because people fail all the time, despite their best intentions and best efforts. People fall short all the time. And forgiveness is what allows you to live life to its fullest.
Forgiveness is not something you do to others. It is something you do to yourself. Those you forgive might not even be asking for forgiveness, they might not even be aware they have wronged, or have been forgiven.
Prayers you offer to God, forgiveness you offer to your fellow human beings.
Just like prayers are first and foremost private, forgiveness is also a private act first and foremost.