If primary died Dec 2018 and I filed our 2018 return as jointly, what do I do with 2019 to retain the history?

First, I would like to express my condolences on the passing of your spouse.  

If your name was first on the joint 2018 Tax Return, you will be able to pull the history forward into 2019 correctly as long as you indicated in TurboTax 2018 that your spouse passed away in Dec 2018.

If your name was not first on your Tax Returns, you will need to start fresh and set up a new TurboTax Account just for yourself.

To do this, at the TurboTax login page, scroll down to Create New Account or click the signup screen link here:  https://myturbotax.intuit.com/sign-up/.

If you have any questions during this process, please comment below so that I can assist you further.