How do I join two subdomains into the main domain in the wordpress?

I set up a website in the wordpress. The website is about Ecommerce online shop. Two shops of different type are to be clubbed together in this Ecommerce shop. One shop is about online trends and Fashion and other is about shop showcasing the friendly items meant for celebration and parties. Both are of different type and so I created two subdomains with subfolders in public html. I have created another subdomain regarding Offers related to both these shops with no subfolder. How could I integrate this to the main domain i.e., the Ecommerce Shop?