TN is not on the drop down list of states for box 15. I can't file until the state is picked....but it's not there. What should I do? How do I pick my state?

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