How to claim a tax credit on self-employment tax?

If you are subject to self-employment tax, you will receive a deduction for 1/2 of the amount of self-employment tax. This is populated automatically in your return and reported on line 17 in Schedule 1. You don't need to do anything to report this deduction.

What credit are you expecting?

There is no credit associated with self-employment tax, only a deduction for half of the tax, as mentioned by @DaveF1006