How do I delete a forum post?
From Moodle Wiki
Navigate to the forum within the course and click on its title.
Navigate to the discussion thread within the forum and click on its title.
Or scroll to the post that you want to delete.
This will delete the post and any posts that stem from it. You may choose to "Edit" the post, if you don't want to lose the branch of posts that stem for this one. Instructors and admins have the ability to delete, edit, and split a post in a forum.
Students may also delete their post, until someone else replies to it, or until the editing period concludes. Note: Most sites allow 30 minutes of post edits/deletes for changes that authors might make.