if you have the plugs,then take the leads off the old plugs,remembering which ones go where,undo the old ones with a plug socket,and replace with new ones,be careful not to break old ones in head,put leads back on and its done.plugs should come with gap already done.
one things for sure,there will be no spark plugs behind the bumper,hes having you on,have you tried looking the other side of the engine to the 3 you have found.