You can easily add and manage administrators to your Azure subscriptions, simply follow the instructions from the Azure Documentation.

1. Sign in to the Azure Management Portal. If you are a user in multiple Azure directories, click Subscriptions and then filter to view only the directory and subscriptions you want to edit.
2. If necessary, create the user in the Azure directory associated with the subscription first. Learn how.
3. In the navigation pane, click Settings, click Administrators, and then click Add.
4. Type the users email address, select the subscriptions you want the user to access, and then click the check mark.