Assuming that this was an excess deferral contribution to the traditional account in the 403(b), the excess contribution must be reported on your 2023 tax return as Miscellaneous income, other income not already reported on a Form W-2 or Form 1099, Other, so that it appears on Form 1040 line 1h. The excess will be taxed a second time when you eventually distribute money from your 403(b). (Double taxation of the excess is effectively the penalty.)
