If I leave box 15 blank from the w2 it will not let me proceed any further. What do I do? I have to put TN and it doesn’t give me that option

Several  states do not have a state income tax.  So these states will not show up in certain drop down lists.   Leave boxes 15, 16, and 17 blank when you enter a W-2 for these states.

Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington and Wyoming

Leave boxes 15 thru 20 blank (empty).  If this does not correct the error then delete the W-2 and re-enter manually.