Add Breadcrumb & Remove 404 Error Message From Category Page

I want to turn my category page below in to a landing page –

https://www.siddhaphysician.com/about/siddhamedicine

I have already made the category page to show the category description, which you can see in the above link.

Now I want to add breadcrumb to that page as well as remove the 404 error message that’s showing up below.

Please guide me on how to do it.

Thanks…