I do not believe a spell will make your hair wavy. There are more natural methods of doing this.
A curling iron and lightly curling the hair can add a little wave.
However there are many whom do not like too much heat or product on the hair.
Using a product, perhaps an argan oil, and scrunching the hair up for a while, then letting it dry naturally can add a wave without the use of heat.
I use the latter method often.