TurboTax doe not apply your 401(k) contribution anywhere. It is only reported in box 12 on your W-2.
If you entered it in the IRA contribution section - remove it - it is NOT an IRA.
Since you are asking from TT Self-Employed, did you set up a self-employed 401(k) plan? If so, Individual 401(k) plans for the self-employed (also called solo 401(k) or solo-K plans) are entered in the Other Business Situations section of Income & Expenses in TurboTax.