Hi Aran, Have you tryed via etc. PowerShell if you have access to do that? Take a look here: https://learn.microsoft.com/en-us/powershell/module/sharepoint-online/remove-spouser?view=sharepoint-ps Else try this way:
- Open your SharePoint site.
- Select Site contents.
- Select Site settings.
- Select Site collection administrators.
- Here you can remove users from the list of Site Collection Administrators by selecting the x icon to the right of the user.
- Select OK to save your changes.
Let me hear if anything of this helps :)