A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Lucy,
Thanks for posting in the community.
For your concern, I am afraid you need to contact your global admin to change the admin role. To prevent specific users to access SharePoint, the global admin or SharePoint admin can try the steps in the reference: Block access to SharePoint for specific users
If you just want to prevent specific users to access specific SharePoint sites, you can ask the site owners to remove their permissions.
Regards,
George