You should be able to manage the notification through this URL - http://localhost:4502/libs/wcm/core/content/inbox.html
Refer the following URL for more details - https://docs.adobe.com/content/help/en/experience-manager-65/classic-ui/introduction/author-env-inbo...
You can try removing "Notify on Abort" and "Notify on Complete" checkbox in below configuration available in http://<host>:<port>/system/console/configMgr
"Day CQ Workflow Email Notification Service"
Hope this helps!