Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
I’ve checked the URL provided on the google test tool and it looks like there’s only one article schema present on that post.
Please see the screenshot below:

Since you’re using the Free version of Rank Math, you would need to edit your post individually and remove the duplicated schema (if any) manually.
But if you’re using the PRO version, we have the bulk editing feature that allows you to update multiple posts and remove the schema markup.

If you’d like you can read more about this feature here:
https://rankmath.com/kb/bulk-editing-in-rank-math/
I hope that helps, let us know if you have any other questions.
Looking forward to helping you. Thank you.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.