Overview
This one-line guide describes how to export Blocks models.
Good News!
You don’t really have to export anything.
All your models are in
C:Users%username%DocumentsBlocks
They’ll reside either in a directory called Models or OfflineModels (I believe it depends if you were signed in or not when you saved your model), as .obj files, and they’ll also have their associated materials.mtl file.
Now just import to your program in any way you import .obj, which pretty much any decent program can do.
Alternative
If you published your object, you can go to the published page and download it there.
Import to Blender
File → Import → Wavefront (.obj)
Import to ZBrush
Tool → Import
