Once a device channel has been created, it can be configured to use as a different site master page rather than the default site master page. For instance, browsers targeted by a mobile device channel could display the content using the oslo master page whereas all other browsers could display the same content using the seattle master page.
The System Master Page is configured for all device channels and cannot be configured for individual device channels.
Follow these steps to apply a master page to a device channel:
Navigate to the site in your preferred web browser.
Select Site settings from the Settings menu.
Select Master page from the Look and Feel section.
Specify which Site Master Page to use for each device channel.
Click on Save.