Unfortunately, those fingers are so close together as to be essentially one object, so any separation is going to require significant reconstruction and sculpting of the area. I would give serious consideration to simply deleting the one or both fingers altogether, and constructing new ones from scratch.
However, here is how I would do this. You’re going to have to remesh and /or dynamesh at points, so be sure you’re familiar with the methods for projecting detail. You should duplicate the scan as a subtool, and perform the work on that, while keeping the original subtool available as a projection reference.
http://docs.pixologic.com/user-guide/3d-modeling/topology/zremesher/transferring-detail/
With the Lasso selection tool active in the CTRL+Shift slot, carefully lasso the pink portion of that finger mass away from the ring finger, and hide it. If you wanted finer control, you could paint a mask around the pinky to where you want the separation to occur, Invert the mask (ctrl-click on empty canvas or Tool>Masking>Inverse), then Hide Unmasked (Toll>Visibility>Hide Pt). Then in the Subtool Menu, select “split hidden”, and split the pink off into its own subtool.
With the two fingers now in separate subtools, this should allow you to more easily close the holes on each. In the original mesh that is misisng a pinky finger, select Tool>Geometry>Modify Topology> Close Holes. This will close the gap left by the missing pinky with some ugly geometry which you’re going to want to remesh (Dynamesh with a high enough Res slider value would be easiest at this point). Then you will have to smooth and resculpt detail on the finger. Depending on how much geometry you were able to salvage for the pinky, you could now try closing the holes on the pinky object and going through the same procedure, although it may be easier just to build a new one from scratch.
Likewise, instead of hiding the pinky portion once you isolate it with the lasso or making, you could define it as a separate polygroup, and run the whole thing through Dynamesh with the “Groups” function on. Note that with Groups on, you will want to turn off Projection in the Dynamesh menu, or you will get artificats around the resulting group seams. You will also need to turn the res slider up high enough to capture the fine detail elsewhere in the mesh, like keeping other individual fingers separate. This should result in two separate closed masses, with a pinky mesh that can now be repositioned with the transpose controls, although again, you may need to reconstruct the pinky depending on how much was able to be split. Without Projection on, detail will be lost, but you’re going to reproject detail from the original after all of this is done anyway.
Once you have rebuilt pinky, you will have to merge the objects back together. If the pinky is a separate subtool, first merge the two subtools together in the subtool menu with the merge down command. Position the pinky mesh as desired, and make sure it is intersecting with the hand. Run the whole thing through dynamesh at high resolution to mesh everything back into one contiguous piece. Then run it through ZRemesher to reconstruct cleaner, low level topology, subdivide the cleaner base mesh sufficiently to hold the poly detail from the original, and project detail from the original onto it via the instructions for subtool projection in the above link. You make want to mask the pinky finger area as projection from the original is no longer valid there, and do any fine detail work there yourself.
