Not sure what you mean by a fridge freezer fitter?
All you need to do when buying a freezer is to let the freezer sit still for 2-3 hours before you plug it in. This is to allow the oil in the compressor to settle after transportation, then just plug it in. Temperature settings should already be set up by manufacturer.
If you want the freezer to built in, then i suggest speaking with a carpenter.
If its a replacement you should be able to do it yourself ,see how it was fitted to the original fridge freezer and then it should be easy to take off and refit.There will be fitting instructions in the user manual