Doing my 2020 return, I realized I didn't take a deduction on my 2019 taxes. Can I prepare that amended 2019 return and not lose the data I've input into he 2020 return?

Yes.  See the following help article for how to amend your 2019 return:

How do I amend my 2019 return?

Not responsive. I've already started my 2020 return and don't want to lose the info. I loaded the CD version of TT 2019 on my laptop and got the amendment done. How do I get the amended information into my 2020 return without losing all the work I've done?