There’s no instant fix
Usually what happens after loan modification is that a Partial Payment Arrangement Made status appears up on your credit report. Unfortunately, Partial Payment Arrangements are considered a negative by the FICO formula, which is why your credit score was adversely affected.
There’s no instant fix for this. The only thing you CAN do is re-build your credit by making timely payments and avoiding any other negatives. You’ll need at least 24 months of consistent, on time payment history to improve your score and get it back to where it was.
More about mortgage modifications here.