There is no way to reverse a charge-off. (This term refers to a loan that was closed, with the entire amount owed taken off the books.) A new loan would have to be created with the same information in the amount that was charged off. You can then use the loans proceeds to pay the charged-off loan.
Tip: When you reopen the loan in CU*BASE, it is possible to reopen with the same suffix if you wish. We would recommend to watch the account to make sure it is reporting correctly to the credit bureaus.