The session feature is inconvenient because it restricts users from editing markups created by others. It would be helpful to have a function that allows only authorized users to edit them. Does such a feature exist?
If you want markups to be editable, perhaps use Bluebeam Studio Projects rather than Sessions - any invited user can be given permissions to edit.
Making this switch limits the collaborative qualities of a Session, though. It all depends on the big picture of what you aim to achieve.
Here's a technical support article that answers this question.
Session Markups locked and can't be edited
Basically, you can only edit the markup YOU made IN the Session. Outside of that, you'd have to download the file, edit it in Revu, and then upload the new version to the Session.
As others have said, you can't do this. You might want to consider re-posting in Product Feedback — your desire for the ability to have (controlled) editability of others' markups in a Session is definitely needed.
Join this discussion to consolidate this request.