It is too late for the stimulus checks from 2020. The deadline to file for that was May 17, 2024. It is not too late to file a 2021 return to seek the $1400 stimulus check for 2021--you have until April 15, 2025 to do that. You have to file a 2021 return and use the recovery rebate credit in Federal Review.
You cannot change the tax year. The current online program is for 2024 only. Only a 2024 return can be prepared online and only a 2024 return can be e-filed.
Online preparation and e-filing for 2021, 2022, and 2023 is permanently closed.
Note: The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac. It cannot be used on a mobile device.
To file a return for a prior tax year
If you need to prepare a return for 2021, 2022, or 2023 you can purchase and download desktop software to do it, then print, sign, and mail the return(s)
https://turbotax.intuit.com/personal-taxes/past-years-products/
You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.
Remember to prepare your state return as well—if you live in a state that has a state income tax.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as certified mail so you will know the IRS/state received the return.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.