Kate, does your key work, can you check if battery is not dead in the key? Was it starting this car before?
You can't really disable the immobilizer. It has to talk to the chip in the key in order to start but for that the key need to be powered. If the key was able to start this car before then the immobilizer knows that key and nothing else is required, the only thing you can do in a workshop is to add/remove keys if they have right equipment for that, also if you have another key did you try to use them?