If you'd like to delete an app, you can click the wrench icon to the right of the app (see picture below) and then "Delete app" in the dropdown menu.
You will be asked to type "delete this app" so that you're sure that you want to delete this app and all its contents.
Remember that when you delete the app, all of its contents will be deleted, and this is not reversible.
Note: You're only able to delete the apps if you created them, or if you are a workspace admin. You cannot delete apps that were added by other users unless you are an admin in that workspace. Learn more about member roles in workspaces here.