State tax filing

It's not illegal to pay tax to more than one state on the same income, but states typically have credits to reduce or eliminate double taxation. If he had worked in actually worked in a different state other than Arkansas, he would generally owe tax to that state as well as Arkansas with a few exceptions. If he lived in multiple states during the year he would have to allocate his income between the states.

The W-2 being from WI doesn't automatically subject him to tax in Wisconsin. On the screen where it asks if he earned income in any other state, the answer here should have been No. This is asking if he earned income while actually working within the state.

Once the amended forms are ready, you can follow the steps in the previous response to set up the amended return. After you set up the amendment, you will go back through the Wisconsin return to make the adjustments. When you get to the screen asking for allocating income, make sure you enter 0 in the Wisconsin column. See the screenshot below for an example.