I don't want Google to show sub domain name (red circles in the below image) in search results. How to prevent Google from showing sub domain name as title in search result?

I don't want Google to show sub domain name (red circles in the below image) in search results. How to prevent Google from showing sub domain name as title in search result?

You don't have control over that. Google will modify the title of the search results as they see fit for the query.
Google isn't showing the subdomain name. I think it's just coincidental that your subdomains are similar (but they are not the same). The text that appears in the title in Google's search results will appear on your page, probably in the title element, or Hn elements, or even elsewhere on your page. (By the formation of the title, I'd guess the title element.)