I recently helped my son successfully fit 2 door protectors to his Skoda Kodiak - one on the driver door and the other the passenger door directly behind. Both genuine Skoda parts. The problem is that the parts are not finely moulded or finished on the latching mechanism that you fit onto the part that is in the door.
Use a very fine metal file to file off the excess bits of plastic - no matter how small they appear to be - to make the bit that you slide over the little rail bit in the door smoother and neater.
Put a very thin film of vaseline on the little bar you are sliding onto and the bit that slides over on the door protector.
Do not open the door very wide at all (15cm max) so the bit in the door sticks out to maximum degree.
Hold the door bit open using a couple of small screw drivers in the notches at the back so you have something to push against (if you don't do this the bit you are trying to fit onto will just press back to the door)
Slide the fitment onto the bar. You do still need to push, but once the first bit goes then it slides on easily.
If you file the tiny bits of plastic off it really does make all the difference. We tried it without before and nothing was happening and we were worried we might break the mechanism in the door. But refining the part with a small fine file really did the trick.
DO NOT try to open the end sticking out prongs with a screw driver or one will break off - though you can still fit the part successfully with one gone. I am not talking about the bar slide fitment but the bits the at stick out at the end. The fitment is just not that well made and is vulnerable. But get rid of the tiny lumps and bumps from the manufacturing process and use a bit of vaseline (not much) and it worked on both very well. (You do still need to hold the door latch out to be able to push against it, but the pressure is less and it worked for us.)
