Hello there, mick123651.
If you're referring to backing up your old customers from QuickBooks Online, you can export your customer list so you can save a copy on your desktop. On the other hand, if you're importing your list of customers to our system, you can use the Import data option and ensure that the spreadsheet is in an EXCEL or CSV file format.
To help you with importing or exporting your customers into QuickBooks online, feel free to use this page: Move your lists to QuickBooks Online.
Let me know if you have other questions. Take care!
