Shift into fwd,unhook it from the shift plate, remove the 2 square screws, pull black plastic sleeve off, remove threaded guide tube, try to lay cable in a relatively straight line
, remove drive, pull slide and inner core out
Using a very deep 9/16ths socket unscrew the cable core from the housing
GET A SOLID CORE FROM A OLD CONTROL CABLE FROM YOUR LOCAL MARINA OR SHOP
Insert core from inside the boat leaving about 4 feet extending.from the outside
Remove outer casing leaving the solid core. slide core into the boat far enough to remove and replace the bellow
Slide core back out and thru the cable sheath and attach a small vise grip in the core end.
While one is pushing and one is pulling insert the cable sheath , apply a bit of sealant and tighten the cable
Depending on your actual setup you may have to help the sheath unscrew and screw back in so as not to twist the cable sheath.
A visegrip with gentle tension on the brass threaded end to assist in turning the casing while tightening