How do I add the after-tax basis for a Traditional IRA Rollover to a Roth IRA if this information is not included on the Form 1099-R?

The after-tax basis to a traditional IRA is tracked on form 8606. If 2022 is the first year that you made an after tax contribution, you will need to tell that to TurboTax and TurboTax will prepare form 8606 as part of your return. If you rolled over an IRA that contains after-tax contributions from a previous year, you will need your most recent form 8606.  If you didn’t track your after-tax contributions on form 8606 and can’t prove them, then you treat the entire conversion as taxable and you don’t get the benefit of the pretax contributions.

you have to enter your "prior years basis" TurboTax will ask for it if you enter a conversion correctly.

@castlevecchio 

Thank you for your response.  It caused me to closely examine my 8606, whereupon I discovered that Turbo Tax had, in fact, correctly factored in my after-tax basis.