Search for the customer you wish to link, select their name and click on "Cust Details."
Under the Accounts section, select the account you wish to link this customer to from the dropdown menu.
If you wish to create a new account, check this article!
Once you have made your selection, the account details will appear and reflect the total account balance.
Be sure to save your changes.
Tip: If you are unable to manage the customer account check the security settings for your job type in Manager Home > Configuration > Security > Manage Customer Account.