Hi there, sumathi. 

Thanks for making your way to the QuickBooks Community. I’d be happy to help find your customers tab in QuickBooks Online.

There are times that your browser is full of frequently-accessed page resources causing unusual responses. You can log in to your QBO account using a private browser. This is to rule out older data that potentially cause viewing and performance issues.

Here are the keyboard shortcuts:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Option + P

Once logged in, go back and try to access the Customers tab.

If it works, it means that you need to clear your browser's cache to offload some data from your browser. This way, your browser would get optimized and get you back into the business.

Also, you can use another supported browser as an alternative.

Additionally, here's an article you can review to learn how to add, edit, delete, or merge customers: Manage customers in QuickBooks Online.

Please let me know if you need further clarification about sales transactions, or if there's anything else I can do for you. I'll be standing by for your response. Have a great day.