There's a way to fix the issue. Please follow the steps below:
1. Have the customer sign up again on this link: https://www.bizplan.com/?prompt=register and use the same exact details and password as before.
2. After successfully signing up, ask the user to go to Accounts (top right corner) > Bizplan
3. Once user gets to the Bizplan section, they should see something like the screenshot below. Ask them to click on "Link Your Account"