I usually have to use a plastic mallet to drive the grip pin back in the frame. It's probably easier on guns that have the plastic(nylon) spring cups, instead of the metal spring cups.
It's also not uncommon to see some small bits of aluminum shavings punched out the far side of the grip frame after whacking the steel grip pin back inside the frame. A bit startling & scary the first time you see it, though.
Making sure the side plate hasn't been tweaked or damaged is pretty important. As is getting the top of the grips seated fully forward under the frame's grip tang, so the manual safety lever has proper freedom of movement. The pics I included in my previous post shows how to tell the difference.