My child graduated from college 2019, & took loans to pay room/board. We used leftover 529 money to pay toward loan. Where do we enter this to avoid penalty and taxes?

If  the child paid Room & Board (R&B) in 2019 and you took the 529 distribution in 2019, you can count the distribution directly toward the R&B.

Either way, you enter it in the same place.  in TurboTax (TT), enter at:

Federal Taxes Tab (Personal for H&B version)

Deductions & Credits

-Scroll down to:

--Education

  --ESA and 529 Qualified Tuition Programs (1099-Q)

Alternatively; you can just not report the 1099-Q, at all, if your student-beneficiary has sufficient educational expenses, including room & board (even if he lives at home) to cover the distribution. You would still have to do the math to see if there were enough expenses left over for you to claim the tuition credit. Again, you cannot double dip!  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, in case of an IRS inquiry.

On form 1099-Q, the 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."