AirPods 2020 replacement

As mentioned in the linked article, your AirPods have to be checked first by either an Authorized Apple Service Provider, an Apple Retail Store or by the official Apple Support.

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Choose one of the service options below to have your AirPods Pro serviced. Your AirPods Pro will be examined prior to any service to verify that they are eligible for this program. AirPods Pro (left, right or both) with a confirmed issue will be replaced. The AirPods Pro case is not affected and will not be replaced.

• Find an Apple Authorized Service Provider.
• Make an appointment at an Apple Retail Store.
• Contact Apple Support.

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copied from: AirPods Pro Service Program for Sound Issues - Apple Support

If your AirPods Pro are not par of the Service Program for Sound Issues, you will have to pay for getting them replaced:

AirPods Repair & Service - Apple Support

Have a look at this Apple page:

AirPods Pro Service Program for Sound Issues - Apple Support