[GolfCoyote]

Its literally like one screw, just pop the cover off the wall and look. My last house had this exact issue.

If the cable is there, there should be one area in your home where the ISP primary ethernet is run, your modem HAS to be plugged into that one. If you want your other ethernet ports plugs in your home to work your modem will need to have extra ports on it and those ethernet outlets will need to be plugged into the modem. Here's a photo of my setup for you to make sense of it better.

Modem (black cable) is plugged into my mesh network router, mesh router (yellow cable) is then plugged into my ethernet switch, my ethernet outlets (the blue cables) are plugged into the ethernet switch. I then have another mesh router plugged into an ethernet outlet downstairs along with whatever else plugged into the outlets throughout my house.