The 1095-A is issued to you by the marketplace insurance you had last year ... you must get it from them.  Start here :  https://www.healthcare.gov/contact-us/

Then to populate the 8962 you can either do it manually or  use the amendment process : 

How do I amend a 2019 return in TurboTax?

https://ttlc.intuit.com/community/tax-topics/help/how-do-i-amend-a-2019-return-in-turbotax/00/123845...