If you have people that buy from your store multiple times using different credentials, you can easily combine those records into one master account. In order to do so, you will need to first go to Customers,
Then, choose two or multiple customer entries that you wish to merge into one and click on Combine Customers, at the top:
A new window will come up that will let you choose, which of the entries to be the Master one:
As soon as you choose the master one, don’t forget to click on Merge Customers, at the bottom and you’re done.