Thanks so much for the replies, @NoahBoswell @mzimmerman @paul_fynn. Unfortunately, I'm on my own. So, I'm the admin, teacher, and IT support for CANVAS since we are a small organisation. I checked the person's role and removed him from all previous training (as an observer and teacher). And it still shows no improvement. But then I check the admin webpage > settings > admins (see attachment). I removed him immediately, and it works! Well, apparently, my former colleague added him as admin a long time ago