Removing the LH or EZK is really very simple: remove cover, undo the LH and EZK connectors, undo two imbus (hex key) bolts that hold the ecu bracket to the side wall, pull the unit a little towards you, undo the coding plug. On a pre-1989 there is also the diagnose connector that needs disconnecting and the 928 after 1988 has the IMR relay plug on the very lower side that needs disconnecting. Then remove the complete assembly attached to the metal bracket from the car. The ecuís are attached with studs that have a M5 nut locking it in place. Remove the nuts and take the ecu from the bracket.
The ecu's have a connector that uses a metal handle to undo it or push it back in place.
First hook the top part into the appropriate slot of the black connector receiver. You'd need to lift the connector in about 90 degree angle to move it into the slot. Then push the connector down. The handle has two puns that mate with a slot and slide into place. Last bit is to push the handle down until it locks.