You can file your 2023 tax return as Married Filing Jointly regardless of how you entered the filing status on the Form 4868 extension request.
If you paid any taxes with the extension request make sure it is included in your 2023 tax return.
To enter, change or delete a payment made with an extension request (Federal, State, Local) -
Click on Federal Taxes (Personal using Home and Business)
Click on Deductions and Credits
Click on I'll choose what I work on (if shown)
Scroll down to Estimates and Other Taxes Paid
On Income Taxes Paid, click on the start or update button
On the next screen select the type of extension payment made and click on the start or update button
Or enter federal extension payment in the Search box located in the upper right of the program screen. Click on Jump to federal extension payment
