How do I change box 15 to Wa.

WA has no state income tax.  Leave all boxes 15, 16,17 blank.  So try picking the very top line in the box above Alabama.    It says Select a state.

If this is regarding your W-2 box 15, WA state does not have an income tax. Leave W2 boxes 15-17 Blank.

You can make the changes as long as you didn't file your return. 

• Log in to your account.
• Select Federal Taxes 
• Click on Wages and Income.
• Select Edit next to Job (W-2)