69 Cutty

I have a 69 Cutlass with a 78 olds engine and tranny. The kick down/ detent cable is stuck. it will not pull out or retract in. i have bought a new one but dont know if that is the problem or if that is the cure.and if it is the cure do i just drop the tranny pan and remove the set screw to replace?? Any ideas would really be a help thanx