I don't have these wedges for my skid plate, just screws. Does this matter?Found some answers for you on a spanish forum to which you have to register, since I don't know if you know spanish I'll translate and summarize a bit.
NKS CLUB - Montaje protector paragolpes delantero - Bricos
1. First you need to clean the under surface where the skid plate will be applied very throughtly.
2. Afterwards when is clean and dry, you need to apply some type of priming liquid that the kit brings on to the surface where you will apply the plate and let it dry for about 15 minutes.
3. Remove the skid plate double side tape from the plate and press it on and hold it still for 2 minutes.
4. You need to drill some holes in the plate that go thru the original bumper, there should be some type of diagram in your docs.
5. Insert the plastic wedges that come with the kit
6. Hammer the wedges in so they go flat
7. Let your car sit still for about 2 hours before driving it for everything to bond well. The original author recommends adding some masking tape to the plate and the main chassis temporarlyto ensure nothing moves or slides during those 2 hours.
Hope this helps, and all credit goes to the autor robertops on the forum linked above.