Filing single this year but was married on previous return. Do I need that return to efile this year or file as if I didn’t have a return last year?

No, you don't necessarily need your 2019 return to file as Single in 2020.  However, you will need your AGI (Adjusted Gross Income) amount from your 2019 return to Efile this year.

This identifies you to the IRS.  Even though that amount was for your joint return, both you and your ex-spouse will need to use that AGI number when Efiling this year.

Click this link for more info on Filing Status Change from Joint to Single. 

If you used Turbo Tax last year you should start a brand new account for yourself and not transfer from last year.  You can not remove a spouse or switch the order of names.

Online is only good for 1 return.  But you can use the same email address for 5 accounts.   How to start another return in the Online version  

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-online/00/25596

Divorced FAQ

https://ttlc.intuit.com/community/family/help/what-if-i-was-divorced/00/25830

Start a new account. Removing a spouse is not recommended

https://ttlc.intuit.com/community/family/help/how-do-i-remove-a-former-spouse-from-my-return/00/27202

Getting Divorced article

https://turbotax.intuit.com/tax-tips/marriage/getting-divorced/L20NC66cf

Video tips for Divorced couples

https://turbotax.intuit.com/tax-tools/tax-tips/Family/Video--Tax-Tips-for-Divorced-Couples/INF14631.html

And see what AGI to use

https://ttlc.intuit.com/community/agi/help/what-agi-should-i-enter-if-i-m-recently-divorced-or-widowed/00/26954