You have to say what your installation is like. If it’s typical consumer cable modem crap that locks up and needs a power cycle now and then, the simplest approach might just be to add a remote power cycle mechanism:

www.adafruit.com/product/2935

isn’t the cheapest but it’s nicely packaged. That’s just a switchable power strip, so yes you’d need some kind of cellular internet or meshtastic or something to operate it.

In the more serious case where your box is at a data center, you generally open a ticket with the data center and ask them to reboot the box (“remote hands”). Sometimes they will do that for free, other times they charge you.