Hello there, northsourcing.
With regard to the steps provided by my colleague AlexV, it is also available in QuickBooks Desktop Premier 2020. For customizing the invoice, you'll want to modify the template or create a new one.
- Go to List > Templates.
- Click the Templates drop-down menu located at the bottom or press Ctrl + N on your keyboard.
- Choose New.
- In the Select Template Type window, select Invoice and then click OK.
- Click the Layout Designer button in the Basic Information window and add the new columns.
- Hit the OK button once done.
You can also check this article for reference: Use and customize form templates.
I'm just a few clicks away if you need more help with QuickBooks. Stay safe.