Is tough place for first time for the task. You just have to knock it in. Trying very hard to keep from knocking it all the way in. 1 you need it for sizing the replacement 2 it can restrict coolant flow. once you have got it out go find the replacement at parts store. Replacement will have a nut in center of rubber plug and be just about same size. Tighten it to expand it plugging the hole. Snug is usually good enough. if you happen to knock it in just move on cause your not getting it out without much wasted energy. it will survive in its new home.