Do NOT change anything on your 2021 tax return that has been filed.

If you want to estimate your 2022 taxes you can either start a new test 2021 tax return using a New User ID or you can use the TurboTax calculator TaxCaster.

Go to the TurboTax website for the online editions and create a New account with a New User ID - https://turbotax.intuit.com/personal-taxes/online/

Go to this TurboTax website for TaxCaster - https://turbotax.intuit.com/tax-tools/calculators/taxcaster/

You can only do that in the Desktop CD/Download program.  You can download the .tax2021 file from online and open it in the Desktop program.  Then you can save it with another name to test in.  There is also a What-If worksheet.  And many other advantages in the Desktop program.  

Thanks for your response.  I have used Turbo Tax Online to prepare my tax returns.  In order to implement your advice, does that mean I have to buy Turbo Tax CD / Download (Mac)?  If so, how do I do that and how much is it?

If you paid for the Online version you can ask if they will give you the download program.  How to contact Turbo Tax
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-contact-turbotax/00/26991

What is the Turbo Tax phone number
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632

Or you can go ahead and buy it.  How to switch to Desktop,

Download the .tax2021 file for free

How do I save my TurboTax Online return as a tax data file?

After you get the program installed the first thing to do before you open your tax return .tax file is to update the program and install any state programs you had. Then open your file. So you first might need to start a fake return to be able to download the state program (go to FILE - NEW).

You can buy the CD/Download here,

https://turbotax.intuit.com/personal-taxes/cd-download