I need to file an amended return for 2019. And I hear you can efile that. But don’t see how to do it? Anyone know how?

Do not amend your 2019 return until the original return has been fully processed.  If you amend before that it can cause confusion and delays.

How do I amend my 2019 TurboTax Online return?

It’s already all done and I got my refund. I realized I didn’t claim all of my deductions so I need to file an amended return 

Do the AMENDMENT process as instructed by TurboTax.

The option to e-File, rather than US Mail, has very recently been added.

That will show up when you are ready to file it.

It's down again. Last notice I got when I tried was that it would be available again late January.

Print and mail in your amended return.  When the IRS opens up e-filing later this month, you will only be able to e-file 2020 amended returns, not 2019.

[EDITED | 1/13/2021 1;32 PST]