Adding a backup Internet WAN on my OPNsense Router

AKA "Spectrum has gone down two weeks in a row and I'm sick of it". I've been borrowing a portable 5G gateway from my Dad for a few weeks, for testing... and two weeks in a row, I've used it as a backup Internet option, since my Spectrum Business cable Internet has gone down. And yes, I'd get AT&T Fiber if I had the option, sadly they don't yet provide service at my studio. So I'm stuck with only one high speed wired provider. I may add on my own 5G backup Internet connection in the future, but we're getting off track.