If you’re using DiscourseConnect with WP Discourse and have the “Update Userdata” Webhook enabled this will happen automatically.
If a user does not have a Discourse username in their Wordpress profile the “Publishing Username” in the Connection settings will be used, which is what happened with that post you linked (you have system as the publishing username).
They did not have their username in their profile, I corrected that and am using the DiscourseConnect
I also tried to update the post, no affect, I then chose to link to the existing and again tried to update, no change to published username, will there be a delay or is there another step I need to take to correct this instance?