Not the
Formentor, but I've DIY'd a Mk3 Octavia and a Mk4 Leon, so in case it helps...
First, the towbar instructions will probably provide the guidance & drawings you need, so follow that. When you pick a towbar, you'll probably find you can download the instructions from the manufacturer's website - try
www.enganchesaragon.com for a look at what's involved.
You'll need Torx bits, sockets and a torque wrench.
I found most of the bumper screws are visible externally. They are all Torx screws on the Leon and Octavia.
Remove the rear light clusters first to avoid scratching and make room for movement. Pull off the flexible cover which covers the screws inside the rain channel for the trunk lid (on the Octavia, a trim hook in the toolkit does this easily, but the Leon is tricky to pull off without snapping clips and refitting is trickier - when refitting, soak the trim cover in hot water first to make it more flexible). On the Leon, two bumper screws are hidden underneath the rear light clusters (one each side).
Then start underneath where the bumper is screwed to the undertray, then the wheel arches.
For the wheel arches, use your fingers to feel around as some are not easy to see. You need to remove the mud flaps if they are fitted to expose some bumper screws. You might need a flexi attachment for your screwdriver to get the right angle without having to remove wheels.
When you're sure you have all the screws out, pull the sides out from the bodywork first and slip some cloth in to prevent scratching.
Then pull gently as shown in the towbar instructions - if you're finding parts won't move, check again for missed screws. Have blocks or something to prop up the bumper as you remove it, and ideally a second pair of hands. As soon as you can fit your hand between the car body and the bumper, reach in and unplug any wiring connectors to sensors etc. inside the bumper.
Removing the rear crash bar and fitting the towbar is straightforward, instructions will cover that.
For the wiring, you need a relay unit. Use a multimeter probe on the connector for the rear light cluster to identify the wires you need to connect the relay unit to.
Quick splice connectors are the easiest way to connect the relay to the car wiring. I use the 12v socket supply in the boot to power the relay (fit the inline fuse as per instructions).
The hardest part of it is getting all the interior trim off and fitting it back again without damage - so if you're new to this, be prepared to spend a few evenings at the whole job and go slowly!
EDIT: What annoys the bejasus out of me about this is that VAG & other manufacturer could pre-wire all cars for very little extra cost per car - saving many hours of labour in retrofitting, and improving safety by making the car's ESC system 'towbar-aware'.
