The quickest way to update the firmware for your AirPods (Pro):

1. Put on AirPods and play music or other type of audio for at least 30 seconds;
2. Put the earbuds back into the charging case and close the cap;
3. Connect the charging case to power using a Lightning cable;
4. Wait 30 munutes and reconnect earbuds to your iOS device;
5. Check firmware version: Settings — General — About — Your AirPods (Pro).

As of today, the latest firmware for AirPods Pro and AirPods (Gen 2) is 3A283.