There is a tool that is a v-shaped metal spring with downturned prongs. However they do not work very well and most people seem to use a couple of screwdrivers and turn anti-clockwise or tap to open the hole.
Let's hope you never have to "use it in anger" so to speak. But it really would be a good idea some day to get the emergency tiller out and give it a dry run, if for no other reason than to learn how to assemble it. When you really need it (in the dark, blowing 40 kts, with a sea running) is no time to learn.