How to connect a replacement AirPods Pro 2 with different serial number?

Did you follow the steps mentioned in this article to connect the replaced AirPod?

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1. Put both AirPods in your charging case.
2. Connect the case to power, close the lid and wait 20 minutes.
3. Open the lid, then do one of the following:

• • If the status light flashes white, go to step 5.
  • If the status light doesn't flash white, continue to the next step.

4 . With the lid open, press and hold the setup button on the back of the case for 15 seconds until the status light flashes amber, then white. If the status light still doesn't flash white, learn what to do.

5 . With the status light flashing white, close the lid of your charging case.

6 . Before tapping Connect on the setup animation that appears on screen, go to Settings, tap Bluetooth, then do the following: 

• • If your AirPods appear after you tap Bluetooth, tap the More Info button next to your AirPods, tap Forget This Device, then tap again to confirm. Continue to the next step. 
  • If your AirPods don't appear there, continue to the next step.

7 . Open the lid, then go to the Home Screen on your iPhone or iPad. 

8 . In the setup animation, tap Connect, then tap Done. AirPods are ready for use.

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copied from: Set up your replacement AirPods or charging case - Apple Support