How do I apply a splatmap to my terrain?

I have a terrain GameObject in-game. I want to apply 4 different textures to it based on a 4-channel RGBA splatmap that I have created in Photoshop. How do I link this splatmap to my terrain object? I've Google'd this extensively for a couple of days now, and all I could find was information on how to create splatmaps. I need to know how to apply it to the terrain once it has been created. Thanks.