You should be able to do this with the pencil icon after you select multiple projects to edit.
There could be some nuances to the edit if you have multiple resource managers that are different across your projects. You may need to identify commonalities between the assigned resource managers and edit those that are the same together.
Examples:
- You have Resource A and Resource B assigned as resource managers on 3 projects you can bulk edit the 3 projects at the same time to remove the one entity.
- You have Resource A and Resource B and Resource C and 1 Project has Resource A and Resource B assigned as resource managers and 2 Projects with Resource B and Resource C assigned as resource managers - in order to remove Resource B you would need to bulk edit the 2 projects together and then update the one on it's own outside of the bulk edit.