You can add after filing; however, once you've filed your tax return do not make any changes until the IRS either accepts or rejects your return.

If accepted, wait until the IRS issues your refund (if applicable), then you can amend your return to add your renters' rebate.  The following TurboTax FAQ can guide you when you are ready to amend:  How do I amend my 2019 TurboTax Online return? - Community

If rejected, you can sign into your TurboTax Online account and fix what caused the rejection.  At this time, you can also add the renters' rebate and re-file.  Refer to the following FAQ for assistance:  How do I fix a rejected return? - Community

I didn't file my renters 2019 Form M1PR with Turbo Tax when I did my federal and state taxes, so can I do that now with Turbo Tax? If so, please let me know!

You will need to amend your return in order to make any corrections. Here's more information on correcting your return. 

Amend 2019 return? - Community