How to create 3 different sites using foreign key

Hello everyone, I realized a site with different tables such as:

• website
• user
• equipment
• peripheral

This site is currently available only for one city or I was asked to create this site for three different cities. Recreating 3 times the same tables does not help me so I will reference my site in each table using a foreign key. But after how can I make to display the desired website according to the foreign key ?

At the level of my code I have nothing to offer you for now because I do not see how to do.