In general private school tuition is not deductible. Why are you entering it? For a state credit? If so, which state?
There is no federal deduction, or credit, for K-12 education. Some states do have a tax break. If yours is one. it will come up in the state interview.
If you took a 529 plan distribution for K-12 education, you, most likely, don't have to enter anything.
You can just not report the 1099-Q, at all, if your student-beneficiary has sufficient educational expenses, to cover the distribution. When the box 1 amount on form 1099-Q is fully covered by expenses, TurboTax will enter nothing about the 1099-Q on the actual tax forms. But, it will prepare a 1099-Q worksheet for your records. There is a $10K limit for K-12 education.
References:
1. On form 1099-Q, instructions to the recipient reads: "Nontaxable distributions from CESAs and QTPs are not required to be reported on your income tax return. You must determine the taxability of any distribution."
2. IRS Pub 970 states: “Generally, distributions are tax free if they aren't more than the beneficiary's AQEE for the year. Don't report tax-free distributions (including qualifying rollovers) on your tax return”.