xtra internet connection on Balance310 via Pepxim/Siminjector

Hi there,
I am using a Peplink Balance 310 together with a Pepxim/Sim injector.
I am using the internet connection provided by the Sim in the sim injector, but would like to use another internet connection I have available as a backup in case sim finishes data or else.
This internet connection is available straight on an ethernet cable, which I would like to plugin directly on one of the LANs of the Pepxim. Is this feasible, and if so how do I create that connection on the Balance 310? so that then I can swap in between and leave one in priority 1 and the other on priority 2? thanks so much!