You are not self-employed with respect to the S corp (except in regard to a self-employed health insurance deduction). You are an employee of the S corp. Your S corp is responsible for making your SEP contribution, up to 25% of the amount reported in box 5 of your W-2, and reporting the deduction on line 17 of the S corp's Form 1120S.
Since you are not self-employed (unless you have a separate self-employment business), you do not need TurboTax Self-Employed. Online TurboTax Premier is sufficient to be able to report your Schedule K-1 (Form 1120S).
A retirement contribution deduction shown on Form 1040 line 28 can only come from net profit reported on Schedule C or (positive) net income from self-employment reported with code A in box 14 of a Schedule K-1 (Form 1065) from a partnership.
