You do not enter "room and board costs using 529 money"
You just enter room and board, without trying to tell TurboTax (TT) where the money, to pay for it, came from. TT will match the college expenses to the 529 distribution. TT will use tuition for the tuition credit before it uses it for the 529.
To get the screen to enter Room & Board, answer yes when asked if you have book expenses.
