its easy to do!!! however i can say that as i have the full windscreen repair kit from where i used to repair cracks and splits!!!
all cracks you need to find the exact spot where the crack ends, then drill into the first layer of glass and not beyond into the plastic laminate!! once you have drilled the exact spot, you then use a punch(

and break the remaining glass at the bottom of the hole, then put your injection gun onto the hole just drilled then inject the UV resin, having done it for years i can do it in my sleep now, however 2 weeks ago i ran out of resin, so thats oin me shopping list for next time im in uk!!
but to answer your original question ,
get a friend or the wife to hold a mirror on the inside iof the screen near the end of the crack, so you can see the exact poiint to drill prob best using a dremel but mount a tiny carbide burr in
it if you drill the exact end of the crack it will stop it spreading once done, inject a small clear silicon sealnt inot the hole this will stop water getting in a making the screen go milky,
