you do not replace it unless it is broken it may be seized up;
get into the bed of the truck, on the opposite side of the handle that's outside the gate you will see a square plate in the inside with about 4-8 screws. This is an "access plate" for servicing the lever and linkage,
The handle lifts up and pulls to levers that travel across inside the gate to each latch on the sides. These levers have pivoting points and joints connected to the handle lever that get rusty and seize up.(or the lever arm could have broken off on the handle)
to inspect, replace or service.....................
remove cover plate screws to remove plate, look inside to see if the lever is broken or seized, if broken remove to take to the dealer to be matched,.. if not broken its seized.... spray lubricating spray here while pulling up on the stuck handle, keep working these. don't be afraid to grab inside on the levers with your
hand and push them side to side. your goal is to free-up all the moving parts,
when done, use thick grease and apply it to all the joints as lubricating spray evaporates and the grease stays for years!
also lubricate at the latches on the sides of the gate.