From the 2023 Schedule C instructions: www.irs.gov/instructions/i1040sc
"Line 19: Enter your deduction for the contributions you made for the benefit of your employees to a pension, profit-sharing, or annuity plan (including SEP, SIMPLE, and SARSEP plans described in Pub. 560). If the plan included you as a self-employed person, enter the contributions made as an employer on your behalf on Schedule 1 (Form 1040), line 16, not on Schedule C."
