Well, I think walmart has three fish that could be called an "eel" but I think young, feeding them all cubed frozen blood worms would work.
It's either:
a) a spiny eel (peacock, tiretrack, fire, etc)
b) Dinosaur Birchir (Sengal) - Sometimes called a Dragon Eel
c) Dragon Goby - Also sometimes called a Dragon Eel
Nother question - what size tank do you have?
In the future, it's best to do a bit of research on the fish you're about to buy before you actually buy it. That way you know what to expect when you bring the animal home.