there is no link of return to modern look on clicking return to classic look . need functionality

In the modern O365 env, we find that there is a small link in the bottom left which says "Return to Classic SharePoint".

I have not found any link, in case you go to Classic mode.

So, i have found this link: https://cann0nf0dder.wordpress.com/2016/06/15/sharepoint-online-new-site-content-page-how-does-it-know-to-render-classic-view-cookies/

Now i want to put that on every page. I am not considering editing masterpage.

I want to put the js code to delete that particular cokkie entry from the browser on a link click which says To Modern Look. How do i achieve that?

Thanks,

Naba