I looked this up on another forum, and was advised the following.
1 cut the sheet to the shape of the window first.
2 before taking the backing sheet off, spray the window with a light mist of weak
fairy liquid solution.(this allows to to slide and move the sheet around the window to where you want it, without it sticking)
3 using a squeegee, squeegee from the centre outwards, removing any bubbles,excess fairy liquid, or folds to the outside edges.
4 allow to dry naturally, apparently the liquid will evaporate.
I did this to mine and to be fair it worked great, and it did dry,and did not ruin the film.
try it on a small bit of film first to make sure yours work with the fairy and the slipperage is good...