@jshin3 , I'm not an expert on subaccounts, but unless the person is an Admin for the subaccount, I believe the only way you could remove someone (like a teacher or student) would be to remove them from all courses they have access to in the subaccount.
I'm going to share this with the Canvas Admins group to see if they have any additional suggestions or recommendations.
I just reread what I posted and I don't think it came through that clearly, sorry!
You can easily remove a subaccount admin from a subaccount. So if the person you want to remove is an admin for the subaccount you can remove that person from the subaccount from the Subaccount settings page. If the person you want to remove from the subaccount is a teacher or student, you would have to remove them from all courses they were associated with in that subaccount.
Does this make more sense? Sorry about the confusion!
To further clarify this, I'd say that users exist at the main account level, and can only be search for (and found) in a sub-account if the person is assigned a course level role (teacher, TA, student, etc.) in that sub-account, or is an admin for the sub-account. I'm always curious about the "why". What would be the use case for removing someone from a specific sub-account?
We have 7 schools. I apply some of my admin accounts at the subaccount level that way a user only has admin permissions for a specific school which is the subaccount.