Only a Group Admin can remove another Admin.
To remove an Admin, follow these steps:
Open the Insight Timer app.
Tap the menu icon (☰) in the top-left corner.
Tap Groups.
Open the Group.
Tap Settings in the top-right corner.
Scroll to the Group members list.
Select the profile of the Admin you want to remove.
Tap Remove Admin.
You must be an Admin to remove another Admin. If needed, you can assign a new Admin before making changes.