You can add and delete apps from your Workspace anytime, as long as you have Admin or Edit access to a Workspace (learn more about Workspace permissions here).
- Click on a Workspace in your Shift sidebar
- Look towards top right-hand corner of your Workspace. You'll see an icon for each app you've added to your Workspace
- Right-click on the icon of the app and select "Delete"
Learn how to add new Bookmarks to a Workspace here.