Step 1 : Enter Email and Registration Number from Email 
Website URL :  https://cbt.darksouls3.com/pc/networktest/Confirmation/Logout/?form_lang=eng
Note : Use Chrome : Clear history & cookies to avoid any bugs . 
Step 2 : Enter your Online ID , Make sure it's correct ID 
Note : If u did not get this page , Try a different browser . 
Step 3 : Click on Send Information
Step 4 : You will get your PS4 Dark soul 3 Stress key linked to your PSN ID : 
Step 5 : Redeem the code on your PSN account