Click on ⚙️ at the top right corner, scroll down until you see Orders and tap Order forms. Here you get an overview of all your order forms.
Find the line with the order form you want to change, click on the pen, make the changes and click on Update.
Find the line with the order form you wish to archive and click on Archive.
Click on Show archived, find the line with the order form you wish to restore and click on Restore.