I want to allow & block ads according to theme of my websites. I want health related ads appear to my site but related category in "General category" is showing " Blocked by product settings" and I don't know how to active/allow this category for my health site.
Which is the name of the theme of your website? Every theme works differently. I'm also assuming you are using Wordpress.
You can block ad categories on a general basis or on a site basis. The screens look identical though, you will need to go to the general ad blocking settings and the site ad blocking settings as in one or the other it sounds as though you've blocked that category. Tricky to describe without being in the account. Note though that if you block health in the general settings then it blocks it on all sites.