broken hyperlinks in previous posts

I understand search engines don’t like broken links in posts so I have searched previous posts (300) to remove or repair any broken links but doing either action in edit, has had no effect. When I go to view nothing has changed.

I have searched this site for an answer and also for a plug-in that would automatically do this, without success. My site is:

I’d sure appreciate some guidance on this. Firstly… Is there a plug-in that will check and repair broken links? and second… am I doing something wrong here? Thank you