How to remove webhooks after OAuth refresh_tokens have expired?

Hi,

Some of the OAuths that we had saved in Database expired completely because it had been 90 days since they were last refreshed. That is fine, but our application kept on getting webhook events from the user whose OAuth already expired for us. We wanted to delete this, but as our OAuth expired, we are unable to do so. How should we approach this problem?

Thanks in advance.