If your client created a new account with a new email address, it's as simple as updating your client's email address in PTO using the Edit client function on the Clients dashboard (i.e. not within your client's return because the email address there is not linked to Intuit Link), and then sending the request like any new client.

If your client retains the existing Intuit account but would like to update the email address associated with that account, the process is quite complicated.  See this discussion for details of the process to follow: https://proconnect.intuit.com/community/lacerte-tax-discussions/discussion/re-client-login/01/115565...