Response:
Access to the Post (Preview) App is exclusively available through an ePost account linked to SwissID. If your current ePost account was registered with a different email address, you are required to create a new ePost account using your SwissID and link it to your existing ePost account.
Procedure:
Log out of your current account in the ePost App.
Register a new ePost account using your SwissID.
Navigate to Profile > Access Management > New, enter the email address associated with your previous account, and send the invitation.
Log in to your previous ePost account.
Confirm the invitation request presented as a pop-up.
Log out once more, then log in with your new account.
You will henceforth have access to all documents from your previous ePost account via the account registered with SwissID.
For further details on linking accounts, please refer to the following resource: