That box should already have an amount from any State Tax you paid on your W-2's or any 1099 forms, that you entered in your Federal return.
Check your entries in your Federal return to be sure you entered the amount of Alabama tax withholding that was reported on your documents.
TurboTax transfers data from your federal return to your state return. If the info in your federal return is incomplete or incorrect, your state return won't be complete or correct either.