replacing window tilt latch

Hello there. Using a slotted screwdriver to get there and 'depress' the tooth so that the latch can get free is really one of the only ways to get the sash to tilt inward for this process. Can you show us a good picture of your current tilt latch? That might give us some clue as to your next step. Otherwise, you do want to be careful--but if in doubt, hiring a local pro may be your best bet. 

Also note that unless you're uncertain the 26-420 was the tilt latch you needed, you may want to send us pictures of an undamaged tilt latch just to be safe. 

Thank you, I understand the problem now. The finger button itself is broken on your latch, so you can't push it in to release it.

Unfortunately, there's not really an alternative means of releasing the latch. These are only designed to work one way. There's not a secondary release or anything. Have you tried pushing against the "tooth" itself? That's the curved part of the latch that extends and retracts when you toggle it, and what's physically keeping the window up. 

If you've tried that and it still doesn't work, then you're unfortunately out of options. The only route forward would be to find some way to cut the latch off, which is no easy feat (and probably won't be cheap, either). I highly recommend doing whatever you can to pinch that tooth in.