You likely can’t find out what key from an export. Logic is key presses are read by the keyboard plugin then transmitted across the event sheet triggers or is just checked by key is down conditions. The issue is with an export the event sheet is purely unreadable data.
When the game was on the site how would players learn to throw grenades?
If trying all the keys didn’t do anything, then maybe you had a two key combination. Worst case with 100 keys it’s around 10,000 combinations but likely you’d only need to check much less. Maybe you copied how another game throws grenades.