In 2018 my spouse and I were separated. I filed as Head of household and he never filed. Can I amend my 2018 return to a joint return and include his information?

[DoninGA]

Yes, you can amend the 2018 tax return to file as Married Filing Jointly.

See this TurboTax support FAQ for amending a 2018 tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/01/27579

[SweetieJean]

But he must agree to this first.