Hi there, s-dutt.
To accept the client's invitation to view the company data, the accountant needs to use their QuickBooks Online login credential.
Please see this sample screenshot for reference:
If they forgot their QuickBooks Online password, they can reset it by following the steps in this article: How do I reset my password for QuickBooks Online Accountant?.
For any additional questions or other concerns, please let me know and I'll get back to you the soonest. Stay safe.