I used to export particular customer bill but now when i export from particular customer many or all customer transaction appear in excel sheet. please help

I've got an option for exporting a particular customer's invoices, rabin.

You can export it by heading to the Sales menu and selecting All invoices as the transaction type. 

Let me guide you through the steps:

1. Navigate the Sales tab and select Customers.
2. Choose the name of the customer to open it.
   
3. Click the Filter dropdown.
4. Choose All invoices for the transaction Type.
5. Select the Date.
6. Tap Apply. 
7. Then, click the Export icon.
   

You can export reports and lists in QBO as well. You can find additional details in this article: Export data, reports, lists, and more from QuickBooks Online.

For future reference, I've also provided a link to further information on using QBO to track balances due to suppliers and customers: Manage outstanding balances for customers and suppliers in QuickBooks Online.

The Community is always here to assist if you have other related issues.