I had an accountant do my taxes previously, but am doing my own this year. Where can I adjust beginning retained earnings for an S Corp on Turbo Tax Business 2020?

Yes, you can transfer last year's PDF into the 2020 TurboTax if your 2019 PDF is a 1040 return generated through TurboTax, H&R Block, or TaxACT software.

Be aware that in some cases TurboTax won't be able to read the PDF, for example if it's password-protected or is a scanned copy of a PDF instead of an actual PDF file.

Please follow these instructions:

1. Open your TurboTax 2020 program and choose New Tax Return from the File menu in the upper left corner.
2. Click Start a New Return.
3. When you get to the transfer screen, click Browse.
4. Navigate to your PDF file, click Open, and follow any onscreen instructions.

I had some adjustments made in my books this year that affected my books that affects the b/s from 2019  what should I do first ammend 2019 before filing 2020?

you do not need to amend the tax return for 2019 if the changes were only to the balance sheet. if there were changes that affected taxable income, k-1's(?), tax basis of owner's interest then you need to amend.  we don't know what the 2019 changes were so we don't know if they have any effect on 2020.  you need to talk to whoever made those changes.