Its from Roblox to unreal, or from unreal to roblox?
If you want to recreate this land as landscape in unreal:
- load this picture to photoshop, gimp, or affinity photo
- make it greyscale and blurr stuff (on new layers etc)
- make it low brightness, and paint in brighter colours where you think mountain peaks should be
- load that blurred image into some terrain generation application like gaea
- work on it add rivers etc (you probably need some tutorials for that stuff)
When you have heightmap (geae also creates water , vegetation etc maps/textures). Get that stuff into unreal make landscape, make materials that use additional layers etc.
ps.
apparently blender has plugin like "depth estimation plugin) well my derp ajj says it may help.
And there is Rbx2Source app/tool that creates 3d mesh out of roblox maps.
Having such mesh exported you can render heightmap out of it in any 3d app.
pps.
I never had roblox installed, so all that stuff is from googling and asking my yellow rubber duck.