It's unlikely that the employer will issue a corrected W-2, because the original W-2 shows what actually happened, and the withheld taxes have no doubt already been deposited with the state.
Your son should file a non-resident AL return reporting the income he earned in AL.
He should file a home state GA return reporting ALL his income and claiming a credit for the AL taxes.
He will wind up with a refund from AL and a hopefully not very large tax bill from GA (after applying the credit), since the two states have similar tax rates.
In TurboTax, be sure he completes the non-resident AL return before he does the GA return, so that the program can calculate and apply the credit correctly.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
