Redirect formula

I have inherited / migrated and an old non wp site with thousands of pages to wp. Every page had an duplicate sub page.

example:

#1: blah.com/organisation/what-they-do
#2: blah.com/organisation/what-they-do/article

#2 contains exactly the same content at #1 so is redundant spam.

Is there a regex formula to redirect all of the /reader page to their parent page?

thanks in advance for any help