where is the heater fan resistorfound on a 1997 gm jimmy

by blower motor passenger side

Are you sure it`s not the blower motor that`s bad ?

The resistor is located in the engine compartment, on the right side of the evaporator case,(if you're looking at it from the front of the vehicle). There, you will see the plug going into the case, remove the plug.
Now with a sharp utility knife you have to cut all four sides of the cover in order to remove the three attaching screws, then remove and replace the resistor.