Please follow the instructions in this TurboTax Help article to enter your solo 401(k).
Hello!
thank you for advise!
should I use Adjusting Self-Employment Income?
The deposits into the 401(k) must be made by the S corp and reported on the S corp's tax return. The S corp takes the deduction. The S corp will report in box 12 of your W-2 with code D for traditional elective deferrals or code AA for designated Roth contributions. When preparing your tax return, you will enter the W-2 and enter amounts in box 12 of the W-2 into box 12 of TurboTax's W-2 form, nowhere else in TurboTax.
The link provided by MinhT1 only applies to individuals who are self employed and you are not self-employed (except for the purpose of a self-employed health insurance deduction). You are an employee of the S corp.
S-corp accountant told me that I should make the contribution by myself and report it in 1040, so it was not reflected in W-2
Perhaps the S corp should consider using a different accountant. Or maybe the the accountant was referring to making personal contributions to an IRA rather than contributions to an employer-provided retirement plan. An individual 401(k) plan for an S corp must be established by the S corp.