When you are entering your education expenses you will be asked if you used a 529 plan to pay for the expenses. If you answered YES, in the next couple of screens you will be given the opportunity to enter the Room and Board expenses.
To enter the education expenses, you would:
Enter education expenses in the Search Magnifying Glass in the upper right hand corner of the screen.
Assuming the student is your dependent and you are the recipient of the 1099-Q:
Enter the 1099-Q before you enter the 1098-T. TurboTax will only give your the R&B screen if it knows you have a 529 plan distribution. Later, in the 1098-T (educational expenses and scholarships) interview, answer yes when asked if you have book expenses. That screen includes the box to enter Room & Board.