If it's a factory fitted job, you probably can't as it will be linked to the engine management unit, but if it's an aftermarket immobiliser, simply follow the wires from the control unit which will be under the dash, (listen for the click when it activates, it will give the position away, or follow the wires from the fob detector), and then open the unit, you will find that the main ignition wire has been cut and the immobiliser connected between the cuts, simply reconnect this wire using a good quality connector. Otherwise, consult a vehicle electrician, mobile ones are best and can be found on Google.
Paul Brooksbank., March 2010