Hi SASUGA,
You only need to enter SEP IRA contributions made through self-employment work. If your employer made a SEP IRA contribution for you, then you don’t need to enter it in your return.
https://ttlc.intuit.com/community/retirement/help/where-do-i-enter-my-sep-ira-contributions/00/26783
Plan contributions for a self-employed individual are deducted on Form 1040, Schedule 1 (on the line for self-employed SEP, SIMPLE, and qualified plans) and not on the Schedule C.
https://www.irs.gov/retirement-plans/self-employed-individuals-calculating-your-own-retirement-plan-contribution-and-deduction
Hope that helps,
Ron G