i need to amend 2021 state tax due to an IRS audit. When i download desktop version, its making me buy all 4 states, whereas i need to amend one state only. what to do?

If you originally had purchased that state, you shouldn't need to pay for it again. If you want to make changes or add a document to a tax return that has already been filed and accepted by the taxing agency, you should follow these guidelines. 

• You must first wait until the initial return is completely processed.
• You will have to use the same TurboTax account that you used for the original tax return.
• Once you begin your amendment, you'll see your original return.
• The refund calculator will start new at $0 and only reflect the changes in the refund or tax due
• Only make changes to the areas of your return that need to be corrected.
• You have three years from the date you filed your return or two years after you paid the tax due (whichever is later) to file an amendment

Select your product below and follow the instructions. 

Amend TurboTax Online 

Amend TurboTax CD/Download 

If you have further problems, please call Customer Service. Here is a link:  Turbo Tax Customer Service