I taped it at the back of my guitar but you can put it almost anywhere.
Warning: if you didn't use a lighter before ask help from some one who did or if you are a child ask help from a grownup about the lighter. Don't apply to much pressure with the scissors, you can cut yourself if it gets out of your control.
And I am turkish so i can make mistake on writing part.
Step 1: Preperation
2) You gonna need scissors to cut the plastic (or a knife but scissors are safer mostly )
3) Most plastics don't stay at the shape you bend them, you can use hair dryer or lighter for the heat ( I used lighter because it looks easier )