If you are trying to dismantle connector on a trailer, The type of trailer connectors I have is the big rubber shell with the flap over the contact pins...
If you remove the hose clamp at the base end one can push the cable forward toward the pins and the whole inner pin-holding rubber grommet will push out. From there you can access the wires, change pins, whatever.
Since mine are all about 30 years old. I had to work a small screwdriver in between the rubber pin holding grommet and its metal shell and apply WD-40 and get that worked around the grommet well. Then the cable may easily push forward the grommet.
When finished, Clean off excess WD-40 and push it back together. Dont pull the cable, That can pull the contact pins out of the rubber grommet. Either use the mating connector socket or a section of tubing or something to press the rubber grommet only.
It goes back much easier than comes apart ! Don't forget the hoseclamp when it's done !
Good luck,
Jakob