Greetings @jenn4 ,
Thank you for posting on the Instructure Community!
Would you mind confirming what "list" you're mentioning? Do you mean your Canvas course navigation? If so, you can go into your course's settings and simply drag the external apps down and it will hide it from your course's navigation menu. This will only change things at the course-level, and not the institution level.
However, if you are talking about the RCE or something else, a lot of these will be global changes by default and will likely require custom CSS or JavaScript within your Canvas Instance's theming to make those changes happen.
Hope to hear back from you soon, all the best!
Noah