Ok - I installed my cup holders this morning, and figured I’d do a how to post... hope this is helpful.
Step 1 - raise the seat to its highest position, and move the seat back forward using the electric adjuster
Step 2 - remove the four retaining Allen key bolts that hold the seat rails to the floor of the car.
Step 3 - tilt the seat all the way back and disconnect the seat motor clips (pic is of the drivers seat)
Step 4 - remove the seat and rails for easier access
Step 5 - undo the 2 13mm hex nuts that hold the front of the seat onto the rail
Step 6 - position the arm of the cup holder over the two bolts and tighten the nuts
Step 7 - Refit the seat, tilt it all the way back and reconnect the motor clips. This is easier if you loosen the wire from the cable clip
When refitting start at the back and move the seat all the way forward to make sure you can get the positioning right for the seat to slot back in place
Step 8 - enjoy having cup holders!