Welcome to the Community, @cschmid.
I can certainly give you some additional information on filing your 1099's. Yes, you can add the missed 1099 to answer your question. This may be done through:
1. Choose Workers from the menu on the left.
2. Select Contractors.
3. Click Prepare 1099s.
If you're filing electronically and have any other questions, here's an article that can help: Prepare and file Federal 1099s using QuickBooks Online.
Thanks so much for reaching out! We're always here to help when you need us.