Use C6250-100NAS LAN as WAN

Hi, I live in a college apartment where the internet is free but my C6250-100NAS won't connect to the internet. The tech support guy said it was weird, because all I need is a router that connects to the wall will a ethernet cable. We tried to connect with a coax cable because that's how I was connected at an apartment last year, but that also hasn't worked. The only time I've been able to connect to the internet somehow was with my iPad (although my PC and iPhone could not connect), and only for two short periods of time. The first, I ended up cutting short because I thought I solved it and needed to reset so that my non-connecting devices could connect. The second just ended up petering out over the course of 2 days.

The tech guy said something that he thinks may work is using the LAN port as WAN port. There's a good tutorial, but only for a different device (https://kb.netgear.com/23693/DGN2200V4-Using-LAN-port-4-as-a-WAN-port-for-cable-ISP-connections). Is it possible to convert a LAN port to a WAN port on my device?

I'm on a college budget, so ideally, I'd like to use this router as much as possible but if it's not, I guess I'll bite the bullet for convenience.