I agree the levy/garnishment would *never* reduce the amount of SS to be reported.  But until we know *what* it was for, we can't be sure it shouldn't be entered somewhere.

I don't think that is what the OP is actually asking tho - I *think* s/he want to know how to enter it to reduce the SS income.   But it's late on a Sunday, and I'm a wee bit tired 🙂