Please follow this doc: https://www.wpbeginner.com/beginners-guide/beginners-guide-to-pasting-snippets-from-the-web-into-wordpress/

Hi can you explain please how did you edit it? thank you

the code should be added in the currently active theme functions.php file. 

Sorry for this noob question but where should I put this code? on the style section?

We may suggest you use the following code:

remove_filter('wpforo_after_add_post', 'wpforo_topic_subscribers_mail_sender', 13);

Just note: in this case, the users will not receive an email for replies even if they've subscribed to this topic. 

Users will get an email in case of registration, mentioning, etc. They'll just not receive the emails for the new replies.

Please navigate to the Subscription page and make sure the "Subscribe to all new topics and posts" is unchecked. And he/she is unsubscribed for the current topic.

https://www.screencast.com/t/ojxmmIbeo69X

Sure the code works fine. It allows you to enable the admin bar for editors without enabling for all members. In case if you want to show the admin bar only for admins, you just need to disable the "Show Admin Bar for Members" options. The option is located in the Dashboard > Forums > Settings > Features admin page.

More info here: https://wpforo.com/docs/root/wpforo-settings/features/

The related topic here, please check it out: https://wpforo.com/community/how-to-and-troubleshooting-2/admin-bar-for-editors-custom-code/#post-16791

Those emails are causing my site to lag because of too much volume. Every time someone replies to a thread. Everyone is getting an email notification which causes lag. Please check the image that I sent for context.

The server from my hosting can't handle it.