If you wish to permanently delete your account, tap on Settings then Account, and select Delete Account. Deleting an account is permanent and all progress will be lost. Account delete requests will be processed within 30 days of receipt.
If you just wish to start over with a new account, consider requesting an account reset by heading to Settings > Account. Just a heads-up—all your items and progress will not be carried over to the new account. The reset is final and can’t be undone, and you’ll be starting fresh on a new server.