Headset earpiece assembly has become detached from headband assembly. The post does not want to go back into the hole on the earpiece assembly bracket. What do I do?

The headband post can only be inserted into the earpiece when the earpiece has been sufficiently rotated. (Note that the hole and post are a 'D' shape, not round.) The installed ear cushion is preventing you from rotating the earpiece sufficiently.

Remove the ear cushion from the earpiece by carefully pulling it off so you do not damage the clips that hold it on or the gasket material between the cushion and the earpiece. There are six clips, three on each side.

Now you can rotate the earpiece into the position where the headband post can be inserted into the earpiece.

Carefully reinstall the ear cushion by pressing it onto the plastic clips. Note that it can only be installed one way with the internal plastic support towards the headband.