The best way to do this is with a small wrench, its tough for sure. what I ended up doing was basically sticking the whole wrench into the C channel and just bracing it with my finger, it ended up working, but annoying
Can I suggest you swap your gas struts around end for end? You want the gas-filled part at the top when the canopy is open. This is so the (very) small amount of oil in the strut can lubricate the seals and also provide a dampener at the end of the stroke.