Adding Textures to a Terrain

Im new when it comes to using UE and have watched a few tutorials on it. However i am struggling with getting textures added to my terrain. My main issue is if i load an official map i can find TLS textures added to the terrain. However if i load my own map and browse for TLS textures in the content browser i get no results. How do i add the TLS textures to my content browser?

Adding Textures to a Terrain