You don't edit, you run the query in the SQL tab that is shown as item 2 here. -->> https://xenforo.com/community/threads/xenforo-mail-settings.221843/post-1683232
Modifying the DB can kill your site. MAKE A BACKUP.
Are you on a managed server? Might want to contact your host.
https://dev.mysql.com/doc/refman/8.0/en/sql-data-manipulation-statements.html
1) Selecet DB
2) Select SQL tab
Some email query examples - Change state as needed:
https://xenforo.com/community/threads/disable-email-notifications-for-all-members.203493/#post-1562815