You don't actually need to push the catch with anything. I can't remember which way it goes but just push the light itself back or forward (which pushes the catch as if you were pushing it with a credit card) and you can pop it out the other side first easily.
The catch is to the rear side of the indicator (ie. at the 3 O'clock position for the passenger side, 9 O'clock for the drivers' side). I suggest wrapping some tape over the end of a small screwdriver, leaving the tip exposed, to protect your paint when prising them out.
