Hello @nht11704,

Welcome to the Community. I can help you get in the right direction with deleting and importing data in QuickBooks Desktop.

Currently, the option to delete customer records in bulk is unavailable. You'll need to remove them one by one by opening each customer profile in the system.

As a workaround, I recommend making these customers inactive all at once. This method allows you to hide them, including the data from the company file.

Here's how:

1. Click Customers at the top menu bar.
2. Select Customer Center from the drop-down menu.
3. Go to the Customers and Jobs tab.
4. Filter to All Customers.
5. Hover your cursor next to a customer you want to make inactive, and then click when the cursor turns to an "X.".
6. Select the other customers that you want to make inactive and then close the Customer Center window.

To delete a customer completely, follow these steps:

1. Click Customers at the top menu bar.
2. Select Customer Center from the drop-down menu.
3. Go to the Customers and Jobs tab.
4. Filter to All Customers.
5. Click the customer name.
6. Press the Ctrl and D keys on your keyboard or click on the Edit menu and select Delete Customer.
7. Repeat steps 1 - 6 for the other customers.

Also, when importing customer data into the company file, there's a specific formatting you need to follow. You'll need to copy the data from the exported file to the formatted spreadsheet coming from QuickBooks.

Please follow these steps:

1. Click the File tab at the top menu bar.
2. Hover your cursor to Utilities, then Import and select Excel files.
3. Select Customers. 
4. The system will open the formatted spreadsheet.
5. Minimize it and open your exported file from QuickBooks.
6. Copy the data into the formatted spreadsheet. 
7. Hit Add My Data Now.

This method will help ensure you have the correct format when performing the process. After following the steps above, you should be able to upload the data successfully.

For additional reference, you can use the following article if you need edit multiple customers simultaneously in QuickBooks: Add and edit multiple customers, vendors, and items.

Drop me a comment below if you have any other questions about importing data or the required formatting. I'll be happy to help you some more.