I'm afraid there's no way to do that. You can perhaps change the email address into an email that you're not using anymore, and never use that Alby account ever again
How can I delete an nostr:npub1getal6ykt05fsz5nqu4uld09nfj3y3qxmv8crys4aeut53unfvlqr80nfm account that I no longer want to use? #asknostr
I'm afraid there's no way to do that. You can perhaps change the email address into an email that you're not using anymore, and never use that Alby account ever again