Give the plastic beads a few seconds to cool, then remove them and mash them together until they form one piece.

The plastic beads should be fairly warm still, but their container will likely be extremely hot. Use care when removing and handling the beads.

Stretch the glob of plastic into a thin strip that will fill one of the gaps between the case halves.

Press the plastic into the crevices and smooth it out with your finger.

If the plastic becomes too hard to work with, you can re-apply heat to loosen the plastic.

Be cautious if you reheat the plastic while it's in the case. Allow cooling periods between reheating so you don't accidentally de-solder any components.