Thanks for your prompt response, @Ganga.

If you'll use the official id, it isn't required to create different login credentials. For that reason, using credentials that are the same as your existing account is recommended. Then you'll have the option to switch to your books and the client's account after signing in QuickBooks.

I'll add this article as your reference on how to manage your clients in QuickBooks Online Accountant. It includes how to create tax returns and review and adjust transactions.

Keep me notified through this post if you have more questions. I'll be around to help. Have a good one!