How to smooth out fuzzy/jittery 3D binary mask

Hello all,

I am trying to create muscle and skin tissue label of human head and using paired CT and MR images to segment.

As you can see the top half of the skin label comes from CT data and the bottom half is from MR(due to unavailability of CT data in jaw section). MR portion of the label is fuzzy or jittery. Is there a way to smooth that part of the data?

I have also shared both the files required to analyse or run experiments with the labels below:

Google_drive_link

Also I can provide more details about the MR data I am working with but due to restrictions I can not share that data.

Any help would be appreciated.

TIA