A polygon group only has one name, the internal name.
The polygon group that should match the Right Foot body part should get the internal name of Apollo's right foot bone: it is probably called "rFoot".

You can check out what the internal names are in the Setup Room: load Apollo, switch to the Setup room and confirm the dialog box that warns you that Apollo contains morphs.
Once in the Setup room, open the parameter dial palette (Object -> Properties) and switch to the second tab.
Now select a body part using the dropdown menu. Both the internal name and the external name appear in the parameter dial palette.
Best to write them down for future reference. Be exact, internal names are case sensitive!

When your list is complete you can leave the Setup room.

Now load your boots prop, go into the Group Editor palette, and check the names. You'll find some mismatches. For example, you may have called a group Right Foot while it should be rFoot according to your list.
Make a new group in the Group Editor, name it rFoot. Then click the button "Add Group" and select the group "Right Foot" from the dropdown list.
Your new "rFoot" group will now contain the same polygons that the old "Right Foot" group does.
You no longer need the group "Right Foot", so select it from the topmost dropdown in the Group Editor and click the "Delete Group" button.
Rinse and repeat until all group names exactly match the internal names on your list.

In this case, there's no need for extra body parts. So the list of groups in the grouping tool should only contain names that match Apollo internal body part names. Any other group should be deleted.
When you've done that, click the button "Show ungrouped polygons". There should be none, if there are, assign them to the correct group.

I prefer the Wireframe and Hidden Line views when working with the grouping tool.

Once this operation is finished, I advise you to save the boots as a prop. I've set up a separate runtime for this kind of intermediary objects; the finished objects (figures or props) go to another runtime.

One of the disadvantages of the Setup room is the limited Undo capability. When you make a mistake, there's often no other recourse than starting over. So - save early, save often!

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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