The the SEPP plan doesn't have to be set up by the IRA custodian, but there are benefits to doing so such as, as DoninGA mentioned, the reporting of these distributions with code 2 so that you won't have to file Form 5329 to claim the SEPP exception to the penalty, but many IRA custodians don't want anything to do with it; Employer plan administrators tend to be more cooperative with regard to SEPP plans.
TurboTax is tax-return preparation software, not software that can assist you in determining the necessary distribution amount. You can determine the annual distribution yourself, request the distributions to be made, then claim the code 02 exception on line 2 of Form 5329 when the distributions are reported as early distributions. TurboTax makes this entry for you on Form 5329 when you enter the amount on which you are claiming this exception. That's all TurboTax can do. Be aware that failing to adhere to the strict SEPP requirements at any time will result in a recapture of all of the early-distribution penalties that had been avoided under the plan, so SEPP plans are inherently risky.
IRS Notice 2022-6 details the three permitted methods of calculating the required annual payment:
https://www.irs.gov/pub/irs-drop/n-22-06.pdf
