Great quality wheelie bar, very impressed with the quality of the item.
a) Start by removing the three screws which form a triangle on the back of the truck. Leave the plastic piece for those screws in place, just remove the three screws.
b) There are three long screws included with the wheelie bar. One of the long screws will be slightly shorter than the other two, and is for the top triangle mounting hole. The other two are for the bottom two mounting holes (on the back of the truck). The 2 longest screws should go through the included 'triangle' plate, through the included metal spacers, and into the bottom of the chassis. The shorter of the long screws fits likewise but at the top of the triangle (through the included 'triangle' plate, through the included metal spacer, and into the top of the triangle).
c) Then remove the two screws from the bottom of the truck near the swing arms. Use the remaining four included short screws to secure the wheelie bar to the bottom of the truck (The shortest of the short screws goes on the very back).
There is a Youtube video below to help with installation though it is in French.