With your photo open in iPhoto, go to the "Edit" icon in the toolbar at the bottom of the iPhoto window, select the "Quick Fixes" tool and then "Retouch." Use the "Size" slider to determine how large the Retouch tool is; if you are fixing a small area of glare, move the slider to the left to make the tool smaller.
How do you remove glare from glasses in a picture?
https://www.youtube.com/watch?v=plOsuoh0eFg
Can you remove glare from glasses?
If the glare isn't directly on the subject's eye, I can often edit portions of it out in Photoshop. Use the patch tool to grab the area and drag it to a clean non-glared skin area. You can also attempt to clone it out by choosing a good area and then cloning just enough of the reflection out.