Open the "Import Customer Acounts From Spreadsheet" function in CM.
Create a spreadsheet template by clicking Create Tempalte.
Next, populate the spreadsheet with the customer account details as needed, removing all unneccessary columns from the spreadsheet.
Next select the newley created spreadsheet.
CM will then verify the accounts listed in the spreadsheet, row by row, and advise of any issues.
Lastly, click Import to push the accounts into CM.