What You’ll Need:
Professional re-tinting or repair is too much to spend on every little scratch or small rip your window tinting is bound to get. As improbable as it may seem, almost anyone with even a moderate degree of skill in at-home projects can repair car window tint. All you need is sufficient patience and care to create a patch in six easy steps. The end result will appear seamless to any casual onlooker.
Step 1 – Locate, Mark, and Cut the Damaged Section
You will need to be careful to remove all of the damaged film, so be thorough when identifying all the area that is damaged. Mark a square around the entire affected area. Next, use your razor blade to slice around the perimeter of what you marked. Use one corner of the razor blade to lift a bit of the film from the glass it has covered. Avoid tearing or loosening any of the tinted film remaining outside the squared area.
Step 2 – Moisten the Section to be Removed
Spray a fine mist of water on the edges of the cut area to soften and loosen the film; do not use window cleaner that contains ammonia. If you spray too much water so that it runs down the window, make sure to blot the excess with a clean absorbent cloth or soft paper towel.
Step 3 – Remove the Film
Use the corner of your razor again to slide under a corner of the square to be removed. Continue running the razor blade under the tint until the entire square has been removed from the window.
Step 4 – Clean the Glass Inside the Squared Area
Spray the uncovered glass inside the cut area, and use a new paper towel to wipe away all film or glue remnants.
Step 5 – Apply the New Tinted Film
Cut a square of new tint in the same color and shade as the old material remaining on your window. The new piece should be at least one inch larger on all sides than the square piece you removed.
Wet the glass again, covering it with a light spray of water from the bottle. Then, with its plastic backing removed, apply the new tint onto the wet glass. Use a damp sponge to press the film down and clear away any bubblesunderneath.
Step 6 – Trim the New Film Edges
Place the straightedge at an end where the new film overlaps the old. Then, following the edge with your razor blade, cut through the two layers—old and new. Use this same procedure on the other three sides as well until you have cut out another square. Holding the new tint in place, remove remnants of the old film that have been cut away; then, press the new film edges into place against the old film edges. It should fit perfectly. Use your sponge to wipe away any remaining moisture and bubbles that you might have missed at the edges and your repair will be complete.
Source- http://www.doityourself.com/stry/how-to-repair-car-window-tint