Requirements:
1. Smartphone or PC/Laptop (preferably Laptop)
2. Onetime acces to the victim's Phone
Steps
1. Install Chrome browser on your device in not already installed.
2. Go to web.whatsapp.com on your device. (In case of Smartphone, ensure you select "desktop version" in settings
3.Go to victim's phone, open Whatsapp, settings, whatsapp web, scan the QR code on your host device, make sure to check "keep me signed in"
voila, that's it!
Note: in case of phone, make sure you do not close Chrome under any circumstances to ensure you are always signed in.