There's no need to call support, you can do it from the Mobile Print Portal app.
Customer documentation for the mobile app is available at: xerox.com/mobileprintportalsupport
Search on "change company" and you'll see the full instructions.
In short, from the app, you should log out then:
On iOS: On the main screen of the Xerox Mobile Print Portal app, select the gear icon on the left below the Next button. Set the “Prompt for Company Code” to On. Select Done.
On Android: On the main screen of the Xerox Mobile Print Portal app, select the Settings button (3 lines) on your Android device. Set the “Prompt for Company Code” to On. Select Done.
When you log in again, you will be prompted for company code.
XMP_Admin
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