Easiest way of fixing rear defrosters?

The defroster is just a piece of wire - when you scraped  your tint off you sliced part of the wire, so the circuit has been broken.

If you can see where the damage is, you *might* be able to splice the wire back together.

Permatex makes a repair kit - available at most auto parts stores.

That is now GONE.  So drive it in the baddest part of town and hope someone smashes the rear window for you so you can claim it under fire & glass insurance coverage.   Or suck it up and go to a glass shop and buy a new window.   Me, I just put liquid dishsoap on a rag and wipe the inside of the rear window and it is smeary clean and does not fog up.

I made a grid repair with conductive paint from a kit.Soon after,the repaired area overheated from it's higher resistance and caused the glass to suddenly shatter while my wife was driving,nearly causing an accident.To remove that window film,use a heat gun to slowly warm it and patiently pull it away.

Before you break the window, be sure your comprehensive is paid up.

Conductive paints are available for small repairs if you’ve just nicked the odd conductor in the grid. Don’t suggest you paint a new one on with it.

Years ago before demisters were standard , you could buy a panel that stuck on, but I don’t think I’ve seen one since about 1973.

Repair is not possible. Replace the window or deal with out it.

You gave yourself the answer you want us to tell you. Doing a job right, however, doesn't always mean doing the easiest  thing. Put that brick back in my yard when you finish using it. Enjoy cleaning up glass from now on. Putting tint on the easiest way resulted in all your problems, didn't it.

If you're talking about an electrical defroster on the glass that has been damaged, the easiest way is to call an auto glass company and have them replace the heated rear glass with a new panel. If you're talking about a mechanical defroster with blower motor, that requires removing all the interior trim and removing the rear seat, which is not at all easy. Given that you've already screwed one thing up due to your ignorance and inexperience, leave it to a professional.

Auto stores sell repair kits with special paint to mend the electric grid.

You will have to replace the window.