When you are a service partner in the app, you can quickly perform service maintenance for a different company. This option is only available for selected parties who conduct on-site maintenance, and it allows for a quick change of company details.

The app will ask you directly if you want to impersonate one of the companies you service when you login.
Tab "partner company" to select the company you want to impersonate. 

If you have already started the app and the pop-up does not appear, or if you want to change the company you are servicing can be found in via te menu