Save reformatted MRI planes

Operating system: macOS Sierra v10.12.6
Slicer version: 4.10.2

I need a guided step-by-step tutorial (or python code) on how to save a volume using reformatted axes.
I have reformatted an atlas to match a home-made orientation in several MRIs. Now I need to export it.

I have found similar topics in the Slicer forum but I haven’t been able to export it.