LED lights are sealed and the LEDs inside the assembly are not "replaceable".
To fix, you must replace the entire fixture.
You might wish to do some troubleshooting before replacing the fixture..
Clean all the contacts on the plug from the trailer and the socket on the vehicle, the connections tend to get corroded. You can use some sandpaper rolled up a few layers and flattened out size it to fit in the plug contacts to scrub the contacts shiny.
Vehicles often have fuses on stop/turn/running lights, make sure those fuses are good, read your vehicles manual to find out the location of those fuses.
Your trailer may also have fuses, if so those may be located near the tongue, follow the tow vehicle to trailer cable to see if you can find a junction and fuse box..
Barring all that, pull the tail lights, move the known working one to the side that isn't working.. If the good tail light works then you know you need to replace the bad one..
If you don't wish to go to the work of troubleshooting you can just throw money at it and buy a new replacement and hope that is the fix to the problem..
If they look like these..
They use a rubber grommet that surrounds the light..
You can pry the light out of the grommet or the grommet out of the RV body..
Although it is possible that if there is caulking around the fixture the caulking may be hiding the screw holes so you will want to remove the caulking ans see what is under it..
