Replacing terrain material

Hi, how can i replace the terrain inside a sphere?
For example lets say we have a size 80 sphere and half of it is inside terrain, how would i replace that terrain material from grass to cracked lava?

I tried using :ReplaceMaterial but the first argument for it is Region3 which is a square/cube.

Found a module that is perfect for this.
Rotated Region 3 Module - Resources / Community Resources - DevForum | Roblox

Nevermind. This rotatedRegion3 module does not work for this. My question still stands :frowning: