Apple has released a firmware update for the AirPods Pro and second-generation AirPods. The AirPods Pro were previously updated to firmware version 2B588, while the second-gen AirPods were on firmware 2A364. The new revision for both models is 2C54. It is not clear what the new firmware does; Apple does not typically issue release notes for accessory firmware updates. The minor revision number suggests that it is a small bugfix or reliability update.
There is no good way to force your AirPods to update the firmware—they do so when they connect to your iPhone, on a schedule determined by Apple. You just have to use them as normal and trust that they will eventually be updated. Some users have had luck by opening their AirPods charging case with the earbuds in them, and leaving them that way (with no music or other audio playing) for a couple minutes. Connecting your AirPods to a power source may also help.
To check your AirPods Pro firmware, open Settings on your iPhone with your AirPods Pro connected. Then tap General, then About. Scroll down below your iPhone’s EID number and you’ll see an entry for your connected AirPods. Tap that to see your model number, serial number, and firmware version.