How do you reset immobiliser in vectra gts 1.8 petrol?

To reset the immobiliser in a Vauxhall Vectra GTS 1.8 petrol, you typically need to use the key fob. Insert the key into the ignition and turn it to the "On" position without starting the engine. Leave it in this position for about 10-15 minutes until the immobiliser light goes out, then turn the key off and attempt to start the vehicle. If this does not work, consult the owner's manual or a professional technician for further assistance.