Please can you erase all the data of customers and invoices.I have mistakenly exported someone others file because of that there are many mismatchs.

Thanks for reaching out to us here, userabhay-tiwari.

At the moment, we're unable to reverse the list and transactions imported in QuickBooks Online. You will have to manually remove the data.

For customers, you can make them inactive by following these steps:

1. Go to Sales > Customers.
2. Select the customer's name and click the Edit button.
3. In the Customer Information window, select the Make inactive button.
4. Hit Yes to confirm.

I'm adding this article for reference: Make a customer inactive and then active.

With regard to the transactions, if they're added on the Banking page, you can batch exclude them. Then, delete these transactions in the Excluded section.

Here's how:

1. On the left panel, click Banking or Transactions.
2. Go to the For Review tab and put a check mark on the transactions you want to remove.
3. Select the Exclude button. 
4. Go to the Excluded tab.
5. Mark the transactions again then click the Delete button. 

Once done, you can import the correct file. You can read this article for more details: Import bank transactions from Excel CSV file to QuickBooks Online.

The other option is to find an application that can help you remove the incorrect customer list and transactions imported in QuickBooks.

To find an app, click Apps on the left panel and search for a keyword like "Delete".

I'll be right here if you have any follow-up questions or other concerns with QuickBooks. Take care and stay safe.

@userabhay-tiwari 

Utilize a deleter tool

https://transactionpro.grsm.io/qbo