How to retrieve the account specifically the admin. when he/she can't access the email add. used?

Thanks for sharing your concern with us, aaying.

You can ask the user to follow the steps below to help retrieve the admin access:

1. From the sign-in page, select I forgot my user ID or Password.
2. Select Try Something Else.
3. Select Talk to an expert.
4. Complete the required fields. Then select Submit to connect to an expert via Chat.

I've got you this article for more details on how to recover user access in QBO:  Recover your account when you can't sign in

If you’re still unable to access your account, I suggest contacting our QuickBooks Care Support. Since this concern requires the pulling of private information, it would be best to handle this in a secure environment like ours. Our support will verify your account and help you with your user log back in.

Here's how you can reach us:

1. Go to the Help menu at the upper right.
2. Select Contact Us.
3. Enter your concern.
4. Click Let’s talk.
5. Choose Get a callback. 
6. Type in your contact info.
7. Select Confirm my call.

You can check out this article for our contact information. Click on the QuickBooks Online drop-down to see the most updated support schedule: Support hours and types.

I'd also like to leave you with these great resources to become more familiar with the different user types in QBO: 

• User types in QuickBooks Online.
• What different types of users can I add to my company?

Anything else you need help with can be answered here in the Community. Just let me know and I'd be happy to assist. Have a good one.