You’ll need blender but I hope this helps
Go into blender and add a plane
Tab into edit mode and right click to subdivide 6 times and press tab again. Right click while the plane is selected and shade smooth
Add a displace modifier
Click new and add a texture
Click image or movie and change it to voronoi or stucci
Now you got decent looking terrain
Go back to the displace modifier and edit it to your liking or whatever they call it.
It looks better
Click file on the top left and export it as an OBJ
