It's actually simpler than you may think. But you do need the detailed printout of your 2020 tax return that includes "all" worksheets and calculation forms.
For the rental, you're looking for two IRS Form 4562's (two for each property). They both print in landscape format. One is titled "Depreciation and Amortization Report" and the other is "Alternative Minimum Tax Depreciation Report". Most likely you'll only need the first one. But have the 2nd one available in case the program asks you for AMT depreciation amounts.
On the 2020 form 4562, for each asset add together the mounts in the "Prior year deprec" column and Current year depr" column. You'll enter this total in TTX 2021 where it asks you for total of all prior year's depreciation already taken.
Also, make absolutely certain the all your numbers agree with what you originally started with. Date placed in service, cost basis, any SDA taken on any listed assets, etc.
