Right-click in the material editor and add a new Noise map.
Then use this map as displacement. There are multiple ways to do it:
You can create a Corona Material and plug this noise map into its Displacement slot.
Or you can apply a Displace modifier to your object and use the noise map there.
I am sorry, but this is basic 3ds Max knowledge, and we offer Corona Renderer help, rather than how to achieve basic tasks in the host software. I would recommend watching some general 3ds Max tutorials and reading the Autodesk documentation.
