2019 form 1098-T reports tuition paid for 2020, for which I received a distribution from 529/QTP in 2020. So I don't want to claim credit for it in 2019. How do I adjust?

You have options here.

Since the Tuition was paid in 2019, and it is on the 2019 1098-T, you can indicate in Box 7 that '..this amount is for tuition in 2020...'.

However, if the Scholarships for the 2020 term are not on the 1098-T, you can enter them separately (if you know the amount), so Tuition/Scholarships balance.

Or, you could wait until next year when you may have a 1098-T showing no Tuition but does have a Scholarship amount, and indicate in TurboTax 'this is not the amount I paid to the school' and enter the Tuition actually paid.

Since this happens often, there are ways to make the reporting balance if you want to make all Education entries in 2020. 

If your 1099-Q distribution was entirely used for Qualified Education Expenses, however, you don't need to enter it in your return.

Click this link for more info on 1099-Q.