This article has a training video on undo button in COMPAS Go. 

The Quote Details view has a “Undo” Button.  What does it do? 

The Undo button can delete any products that have been added to a new quote with status of Editing ON. Editing OFF puts a copy of the quote on the server. (Checked in) Editing ON will show the server version and a user has control of the quote. (Checked out) Users will get a pop-up warning when clicking on Undo.

Undo is like “Get Latest Version” where the quote would revert to the quote last checked in. (Editing OFF).  

Switching between Editing OFF and Editing ON will save your work. You are saving the quote to the server.