Hello there, @ldubach ...
Sorry to see that your question has been sitting out here in the Community for so long without a response. If you are asking about LTI external tool apps that are in your course, the ability to delete them will depend on how they were originally added to your course. For example, if you go to one of your courses and click on "Settings" >> "Apps" tab >> "View App Configurations" button, you will see a listing of the LTI external apps that have been installed (and are available) in your course. Some of those have a padlock icon to the left of the app name along with an info "i" button on the right. Some apps, however, do not have a padlock next to them and have a gear/cog wheel icon next to them. The apps listed with the padlock icon have been installed at the Canvas account level (most likely by your school's local Canvas administrator or someone from your school's Online Learning/eLearning department) cannot be uninstalled by you. They can only be uninstalled at the admin level (not the course level) by your school's Canvas admin. But, keep in mind that if an app is uninstalled at the account level, it is removed from all courses in your school's Canvas environment...not just your course. So, you'd want to maybe have a conversation with your Canvas admin about that. For those apps listed that do not have that padlock icon, those are apps that you can remove on your own. You can click on the gear/cog wheel icon, and you should see an option to "Delete" the app from your course. Since this is a "per course" action, you'd need to carry it out in other courses where you're not wanting to use that app any more. Additional information on all of this can be found under the section "View App Configurations" (about half-way down) within this Guide: How do I use the Canvas App Center in a course?.
I hope this will be of help to you. Sing out if you have any other questions about this...thanks! Take care, stay safe, and be well.