A IRA is not the same as a 401K. If you contributed to a 401K it will be on your W2 box 12. You already got the deduction. 401K come out of your checks pretax and have already been deducted from the wages in box 1 and you can't deduct it again. See box 1 should be less than boxes 3&5.
In the subject line, you say IRA, but the body of your question says 401(k). These are different plans.
If this is a 401(k) plan offered through your employer, it is already listed on your W-2 and will be recorded when you enter that form. If it's an IRA, go to Federal > Deductions and Credits. Only Traditional IRA contributions can be deducted; Roth IRA ones cannot.
If you have a 401(k) through your employer, your contribution is reported in Box 12 of your W-2 with the letter code D. Because your contribution is included in your W-2, you do not re-enter it in the retirement section.
If you made IRA contributions in 2021, please see Where do I enter my IRA contribution?