Viewing Prior Return

Access to prior year returns.

You can get a free transcript from the IRS:   

https://www.irs.gov/individuals/get-transcript

How do I get a copy of a return I filed using online TurboTax?

https://ttlc.intuit.com/questions/1900748

How do I get a copy of a return I prepared using desktop TurboTax?

https://ttlc.intuit.com/questions/1900639

How to upgrade to PLUS

https://ttlc.intuit.com/questions/3404582-how-do-i-upgrade-to-plus-if-i-already-filed-my-2016-tax-return

https://ttlc.intuit.com/questions/3796106-why-do-i-have-to-pay-to-access-my-prior-year-return

https://ttlc.intuit.com/questions/3355524-when-does-access-to-my-prior-year-turbotax-online-returns-expire

Note:  While you still can, print a copy of your current year tax return and save it as a pdf, too.  That way you will have it when you need it for school, a loan, etc. without going through a lot of aggravation to get it.

Can I add forms to my 2019 tax form after submitted

No.  If you filed with incomplete information then you have to wait for the return to be processed and then prepare an amended return.  What form are you trying to add?