I wanted to contribute an additional amount to my 401k to reduce my income but when I enter the additional amount it does not change my tax due

Are you referring to a deductible Traditional IRA contribution?

Everyone is eligible to make contributions to a traditional IRA, but a tax deduction for those contributions may not always be available. You may need to reduce or entirely eliminate your IRA deduction if you or your spouse:

• contributes to an employer-sponsored retirement plan, such as a 401(k) or 403(b)
• has Modified Adjusted Gross Income (MAGI) that exceeds annual limits

In TurboTax Online, traditional IRA contributions are reported under Deductions & Credits, then Retirement and Investments, then Traditional and Roth IRA Contributions.