Performing Minor Edit in STL

Hey Guys - I've got a model which I made (well, honestly assembled from other sources) within TinkerCAD which is two hands on a desktop stand (see attached). Due to preference as well as the size of my printer bed, I'm wanting to shorten the wrist of each hand. Having used CorelDRAW in the past, I thought this would be simple; but cannot figure it out despite trying it in a variety of software including TinkerCAD, Meshmixer, Blender, FreeCAD, & 3DS Max. Thought I'd post here as I'm sure it's simple once you know how to do it.Any suggestions? Thanks!

Both meshmixer and tinkercad have easy solutions.

Meshmixer, import the model. Use Edit, Plane cut and use the rotation handles to spin the plane to 90 degrees. For the first cut, change the result to "keep both" in order to provide uniform chopping. When you select Plane Cut, the program divides the model in half, making a symmetrical model an easier task. For my test, I dragged the plane to the 100 mm mark and performed the cut. Selecting Plane Cut a second time, I moved the plane 100 mm in the opposite direction and did not use the keep both option.

This resulted in a two part model, one part with both hands, the other part with most of the wrist and arm removed.

There's something amiss with the model as there were four or five other artifacts that were then removed with the object browser.

Export as desired.

For tinkercad, the imported model will drop into the center (huge!) but that's not important. Once imported, select the box (hole) from the toolbar, drag it anywhere. Size it to be as tall as the model, plus a bit, as wide as the widest part, plus a bit, and a known amount of thickness. I used ten for easier math.

Select both items, select the align option and align left/right and fore/aft. No need to change the Z alignment as they should all be on the work plane.

Select only the hole-box and drag it to the desired location, making note of the distance indicator as you drag. Again, I used 100 mm for my reference. Once in place, use copy/paste to create a duplicate. In order to be certain of the placement, I dragged the newly created box to match the position of the source box then released the mouse. Using the 100 mm reference, I dragged one of the hole-boxes in the opposite direction, then another 100 mm and an additional 10 mm to compensate for the box thickness. Hold shift to prevent Y movement while dragging in the X direction, just for convenience.

Once in place, resize the outer portions of the hole-boxes to encompass the remainder of the model. Select all, Group and you'll have your model ready to export.

Because it's easy to share from Tinkercad, I'm attaching the link to the now-public model of the above crop:

https://www.tinkercad.com/things/2U2RIPzuIwO

Giving it a shot later on - Thanks for the reply!

I Reduced it using TinkerCAD to fit on my bed