Defrost the frozen poi at room temperature for a few hours. If you're in a hurry, put the bag of poi into a tub of warm water. You can also microwave the poi on the defrost setting...if you do this, remove the poi from the bag first (in case you blow it...you don't want the plastic and ink melted into your poi!), and keep checking the poi so it doesn't start cooking.
Once the poi is defrosted, break it up by hand into small pieces...the small the better. The more you break up the poi at this point, the less stirring and mixing you'll have to do later. Place the poi pieces into a pot and add about 3/4 cup of water for each pound of poi. (...if in doubt, use less water...you can always add more water later). Stir constantly on low heat until the poi is smooth. Cool to room temperature to serve. If the poi is too thick, add a little water.
To store unused poi, place in a bowl and put a little water on the surface of the poi before refrigerating. This will prevent a "crust" from forming on the top. Poi that has been refrigerated will get thicker, so when you are ready to serve it again, just mix in the water that has been sitting on the surface (and add more water if necessary).