how do I replace the fridge thermistor on my hotpoint mistral?

I have a Hotpoint Mistral F/F Model FF73S. The freeze fine, but fridge not working. I have been advised to change the fridge thermistor.
I have tried the following. When I unplugged the yellow thermistor I got error code E7, and no fan and no freezer start up. When I unplugged the green thermistor I got error code E1, and the fan at the back of the freezer started up. I am not sure which thermistor needs replacing. I can see where the colour coded end plugs in but can not work out where the other end needs to go. Can you help me with instuctions on how to fit a fridge thermistor, please???????