How do I disconnect my AirPods from someone else's iCloud?

They will need to perform the steps described in If an item or device is connected to another Apple ID - Apple Support. You can't do it on your end.

If you can't remove the device or item and unpair it from an Apple ID you should reset it. When you reset your device or item, it won't provide its location information to the previous owner. However, you still won't be able to pair the device or item with a different Apple ID.