Hi @Sherazad Ahmed ,
You can assign a user to a SharePoint admin role in 2 different ways:
- You can go to the user's details and Manage roles to assign a role to the user.
- Or you can go to Roles and select the role, and then add multiple users to it.
For details, you can take a reference to below articles.
Assign admin roles
About the SharePoint admin role in Microsoft 365
If you mean that you want to add a user to a SharePoint Online site admin, please refer to this artice: Add or remove site admins in the new SharePoint admin center.
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.