Place the new Airpod - along with the old Airpod that is still working - into the charging case. Charge your Airpods for about 15 minutes using your charging cable or Wireless Charging Station.
Open the lid of the charging case and close it again. Wait 30 seconds and open the lid of the charging case.
Navigate to "Settings" on your Apple device. Then select "Settings -> Bluetooth" and click on the info icon next to your AirPods. Select "Ignore this device". Finally, confirm this process again.
The following steps will perform the AirPods reset:
Check the status display. To do so, open the lid of the Airpod charging case. The status indicator now flashes yellow.
Press and hold the setup button on the back of the charging case for a few seconds until the status indicator flashes white.
Close the charging case and keep it closed for a few seconds.
If the status indicator continues to flash yellow, repeat step 5. For better results, charge the Airpods again for 20 minutes from the power source.
If step 5 was successful, all you need to do is open the charging case next to your Apple device. The AirPods setup animation should appear on your device. All you need to do here is tap "Set Up" and then tap "Done".