The connecting plug has a hook at the cable entry end, so you need to press down the retaining clip at the other end, then swing that end away from the socket, as you lift that end you will reach a point where you can maneuver the hooked end (cable end) out and away, releasing the plug. It's fairly easy once you have done it once, but you may need to use a bit of force as the cable assembly is a bit stiff. In the event that you have pressed the release clip and cannot swing that end of the connector up and away you may need to use a screwdriver to assist in levering that end of the plug away from the ecu socket (while keeping your finger on the release clip)
