Node assets are disabled?

Godot Version

v4.6.1.stable.mono.official [14d19694e]

Question

How do I enable the Terrain3D assets?
I am following a tutorial on how to add an asset so I can paint the terrain a certain color. the instructions tell me to change the 0 to 1 and then edit it? but it's disabled,

Did you enable the addon in the project tab?