Move the two levers and the seat will lift up, make sure you disconnect the seat heaters if you have them and take seat out of the car. The locking pump is in a foam covering near the outside rail under the passenger seat. if it is the origional you will have hoses plugged into a plenum on the pump. The yellow lines are for central locking, the orange for back up rods, the black for trunk lid grip, the gray for orthopedic backrest, and the clear is for backup engine vacuum when it is not running. The fuel door is also part of the lock and unlck system. Your head rests are probably electric, the pump does fail eithe thru water, moisture, brushes, etc. they are typicly available for about $500
There are three cables from the door locks, from the alarm system, and door sensors. The pump sets its start command from the key cylinder microswitch. It also gets a command from the infrared control module (remote) via the sensors on the door and trunk. The pump runs untill it reaches 600 mbar in the lock and unlock function, but no longer than 10 seconds if there is a leak. It provides pressure to unlock vacuum to lock. The secondary timeout for lumbars etc is 60 seconds, but will run to replenish the pressure for the lumbars and vacuum for the HVAC which is stored in a reservoir.

I you have the newer universal pump there is no plenum rather a series of fittings and "t"s
The US versions had a standard soft close option which would draw in the doors, that pump is located on the top of the drivers side rear wheel next to the fuel tank which has a number of red hoses going to it.