Go to the left part of Valor Lakefront where there is the little pool and a house a little further north. On the right side of the house, you will see a Rock Climb path you can take that is quite hard to find from a distance. It will take you to another Rock Climb path, followed by another and another. Once you have gone through, you will be next to the house of the girl who lost her Suite Key. There will be an item there that contains the TM for Dream Eater.
Here is a map to help you if my directions were too confusing.