I'd be delighted to walk you through the steps on how to add an admin user in QuickBooks Online (QBO). The company admin access allows the user to do all the task in your account except editing or removing your master admin's access.
Here's how to do it:
Go to the Gear icon. Then, select Account and Settings.
Select Manager Users.
Click Add user button.
Select Company admin as the user type.
Fill in your admin's contact info and click Save.
After saving, this is how your user list looks like. Status should be Invited. Once the added user accepts the invite, the status will be changed to Active.
Here are some resources for additional information about managing user in QBO: