How do you forgive someone who won't acknowledge they did something wrong?
I find thinking about forgiveness of financial debt helps in thinking about forgiveness of moral debt.
For example, say someone owes you a thousand dollars, and you decide to forgive him his debt. What does that mean?
It means that you tell both him and yourself (and anyone else who has a need to know) that he doesn't owe you the money, and then you erase the debt from your books and from your mind. (It doesn't mean you pretend he paid you back; your own creditors won't be happy to be paid with that imaginary money. Nor does it mean you can keep reminding him of your forgiveness; that's just converting what he owes you from money to gratitude.)
For his part, the debtor is free to accept your forgiveness or not. He should repay, not the original financial debt, but the new debt of gratitude. But he might choose not to be grateful, to treat your forgiveness as nothing more than his good luck. He can also choose to live as though he still owes you the money; he can even try to pay you back.
All that's on the debtor, though. If you've truly forgiven his debt, whatever he does won't change what you've erased from your books and your mind.
So what if someone owes you a thousand dollars, and you want to forgive that debt, but he won't acknowledge that he owes you the thousand dollars? It's not much different on your part. You erase the debt from your books and from your mind. He, obviously, won't respond with gratitude, still less with an attempt to repay you. But all that's on him.
I think this all carries over pretty much directly when forgiving a wrong that's been done to you. You tell the one who wronged you, and yourself, that you forgive him. (You might also need to tell other people who have noted the wrong done to you in their own books.) That he will not acknowledge the wrong he has done is something else you would need to forgive, if you really want to forgive him. (Otherwise, it would be like pardoning someone for robbing a bank, but still bringing weapons charging against him.)
I suppose you should make a good faith effort to convince him that he has wronged you, both for his own sake (being forgiven is good for the soul) and against the chance that he might go on to wrong someone else (or even you again) in the same way in the future. But you can't force him to acknowledge his wrong, and what can't be done can't be obligated.