If you get an email stating:

"The following user has requested to be linked to a new reference number"

This means that the user has logged into their account and has requested to have another account linked to them. You can manually link account by going to the "Web Search" and finding the user by searching for their email. Before linking any accounts, manually confirm that it is the same person (i.e. same name and SSN). If you choose to link the requested account to the existing account, simply enter the account number on the right side:

To unlink an account simply click the un-link button on the right of any account. Note that when the user logs back in an unlinked account that has not since be associated with another account will be relinked because it matches the criteria. Accounts are usually unlinked so that they can be linked to a new account. So the order of events is important.