The 1040X does not have that box. You must just write in the reason for amending that it is to change the status, but it will probably have not affect on your tax or stimulus since the is no longer using the 2019 return for the stimulus - they are using the current 2020 tax return now. 1040X takes 6 months to process and your 2020 tax return will be filed long before the 1040X is processed anyway.
Just file a 2020 tax return and answer the stimulus questions and any stimulus owed to you will become part of your 2020 tax return.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
