How to put hands in arm Peg holes at are too big?

To contradict what anti said lol-

Put a bead of superglue on the hand's peg or shaft, let it harden completely. Test the fit, add another bead if needed, repeat until happy with the fit. Usually only takes a few minutes for the superglue to harden, but you can speed it up with accelerant.

I don't like hot glue, but it works as long as you use a little vaseline to reduce friction/stickiness once it's cool.

Well, still, super glue and not hot glue, regardless of how you do it.

I've used super glue with the brush applicator to build up the thickness of the peg. You don't want to just glop on a bunch all at once, brush the glue on in layers, allowing at least a couple hours for each layer to dry. It's a time consuming process, but would probably work better that trying to get hot glue into the relatively small arm holes (depending upon the figure).