You should be able to see an "edit" button on the upper right (near the thumbs up button) on the top post of a wiki. Some have permissions for anyone to edit, some just allow staff to edit. So click on some and see if any let you do it. If you're just doing it for the scavenger hunt, change something subtle like adding a space at the end of a paragraph or something. Then hit submit and it should be good to go!