Eresan the RG6 should have a metal connector on the end. If you look into the end of the connector you should see a bare metal copper wire. It needs to be straight. That wire inserts into the center hole of the connector on the outside of your trailer and then you tighten up the nut on the cable screwing it onto the cable connector on the trailer.
If the center wire is bent you won't be able to put them together. If you can't straighten it out then the cable will need to have the end trimmed off and a new coax connector installed.
2015 GMC Sierra 2500HD Duramax