Reattaching rubber neckband to plastic housing?

The glue holding the rubber onto the plastic side containing the power button on my Beats X is failing, causing it to become detached. Ideally I'll like to fix it so that it looks as good as new, though I'm not sure what adhesive to use, or how to make the rubber fit properly around the plastic again.

Also the black bit (no idea what it is even called) that covers the speaker channel on one side has gone missing. Is there anything I can use to replace this part?

Any advice would be appreciated.