Write some php code inside a website page ,about free users to become 7 days trial users

I have a page visible only to pro members. ([login to view URL]) I use a plugin for that. (paid membership pro) A conditional in php inside my PRO page redirects non-pro members to the free page. By the same conditiona, PRO members are allowed l to have access. I want you to get the appropriate variables from the database (i attach screenshots), and add a new condition. I want all free users to have a 7 days trial period. so i want this code give them access to my pro page by subtracting the today date with the stardate variable (which is the date they signed in as free users). I understand the basics but I am not a developer , i just know what i need, :) That means that i will leave you free to work without disturbing you with "how to do it" and such things. I attach you screenshot from phpmyadmin and the part of the code just to let you have full control on the information. I have my website 2 times installed. 1. the live site . 2. the sandbox testing enviroment. You can safely work in the testing website and then paste changes to the live.