reverse mouse buttons

hi ive been playing this game for a few years now and never had a problem. but when I plugged in a new mouse to my laptop and went to play left click was move and attack and right click was to buy things etc, how do I fix this as I cant figure out how, my mouse primary button is right so everything else is working fine except lol, ive been into a custom game to try and change my button load out but for some reason I cant change my left click to become move and attack, plz help.