Turbotax shows my return as completed ready to mail but I have a new 1099 to add. How can I reopen from the ready to mail status?

If you've already mailed the return or have e-filed already, then you need to file an amended return. Turbotax has an option for that.

If you have NOT mailed it in nor e-filed, then go back to the tax return on Turbotax. Open up the return. Click on the tabs for FEDERAL TAXES near the top (just under the red checkmark). It will bring you back to the beginning. You can add any new forms you need now. Usually, when I realize I need to add in a new form, I go through everything one step at a time to make sure it is all correct and updated.  It should be fine. Go through the State Return as well so that any changes are sure to trickle down to that return as well.  Then print out once more. Should be good to go.

Thank you for the fast response! The problem remains, it thinks my fed and state are ready to mail and there is no option to reopen. I'll try to paste a look at the page:

Click on Tax Home; your return should be unlocked.   If it is not, scroll to the bottom and click on Add a State - but you don't have to add a state, you will be able to modify your return.