VBM on SPM12 with Vol2Brain's output

Hi everyone!
I used volbrain to segment mri scans and now I am using SPM12 to carry out the Voxel-based-morphometry, to compare it to the Source-Based-Morphometry, and right now I am stuck with it.

I read an article about doing the VBM after VolBrain segmentation, and they mentioned that they applied DARTEL to the images before conducting the statistics, so I contacted the first author of that paper to ask about how they did it. She told me that I would need to undo the linear transformation and apply a 4°spline one to the segmented images, but she didn’t recall how to do it.

Right now, I am struggling to find the instructions on how to take these steps, and if anyone knows how to carry them out, I would highly appreciate a few words on them.

PS: I thought about downloading VolBrain’s outputs in the native space and to apply only the 4°spline transformation, would that be an option?

Thanks everyone!