Multisite for different countries – how to load global site before redirecting?

Hi,

I am working on a site that will have 4 variations based on countries – India, Australia, Africa and a global site for rest of the world. The pages that will be different will be a few static pages and some products. So few products will be available to all customers and some would be specific to the countries. I found this plugin https://codecanyon.net/item/woo-multisite-product-category-sync/19560922 that will help me have common as well as separate products. I have another requirement for which I have been looking at forums but am not able to figure out:

When someone searches for my site (lets called it priyanka.com); I want the global site to open up with a pop-up asking them if they would like to switch to country specific site. On selection, user will be directed to india.priyanka.com, australia.priyanka.com or africa.priyanka.com. Also, at any point of time ; I want a dropdown somewhere in the header that shows which site is loaded and an option to change (Behaviour similar to when you visit https://www.sc.com/en/).

Will appreciate inputs on how to do this.
Thanks,
Priyanka