Welcome and thanks for dropping by the Community, @tmrhine.
Since the SEP IRA contribution is reported on line 28 of Form 1040 (long form), not on the Schedule C itself, the option to categorize it in QuickBooks Self-Employed (QBSE) is currently unavailable.
You need to manually mark it as a personal expense or transaction and need to be accounted for when filling the Form 1040. Before doing so, I highly suggest consulting your accountant for further assistance with the process to ensure everything is on the correct line.
Just in case, I'll add these articles for more information:
I want to make sure everything is taken care of for you, so please let me know in the comment below if you have any other concerns. I'm always here to help. Have a great rest of the day!