Currently Amazon don't have function to update expire token on developer end but Amazon will send you email with a reminder to re-authorize token, 30 days before the expiration.
Please follow the below steps to re-authorize existing token when its expired or going to expire. We suggest you to re-authorize the token before its expire. If you don't re-authorize token than it will stop getting orders, dispatch and other updates.
Login to your Amazon Seller Central account and From left side menu select -> Apps and Services and Manage Your Apps
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Please open the ticket for your enquriy.