i need to enter my state into box 15 of my w2, however tennessee is not in the state list

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

Did you have anything in boxes 16 and 17 on your W-2?

If not, then don't enter anything on box 15 either.

This is sometimes caused by software that automatically enters the state initials into box 15, even though there is no income tax in that state.