If you have not filed your return yet, you can change your filing status.

1. Click on Personal Info, You & Your Family,
2.  Scroll to Your Filing Status,
3. Click Edit, 
4. Check the box Change my filing status

If you already filed your return and it has been accepted, you would need to amend your return to change the filing status.

Click on the following link for information about amending your return.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-2021-return