1) Open case
2) Open Settings
3) Go to General > About > Scroll down to find your AirPods name and click it - if not updated out of sudden then wait in this window
There is no sure way to trigger the update. I've always just used them for about 15 minutes then put them back in their case and plugged it into power. I leave them next to my phone and check back in 30-45 minutes later and they usually have updated. You can read through the thread below for other update techniques:
They update automatically and sporadically. The directions tell you how to set things up to update, but I've never had them reliably update just by doing that (or maybe I wasn't patient enough). Eventually they'll update.