SyncEtc, the company that makes Tach & Go, handles this request.
If you can no longer use the email address you sign in with, SyncEtc can change it for you. We email a link to your new address first: open it to send us your request. Then SyncEtc telephones the number your organization has for you, and makes the change at least 24 hours later, telling both addresses first. It can take much longer if we can't reach your organization's administrators, who must confirm who you are before we change anything.