If you used Turbo Tax last year, the ending balance should have flown to the beginning of the following year. Certain numbers cannot be changed, unless you change the prior years return. You can create a fake 2020 return with the ending balance you want, and have it flow through, but I would not advise that.
If your issue is the ending balance (reason you want to change the beginning), just work with the "contribution" or "distribution" amount to tie the final number out to what it actually should be.
