Before you proceed, you need InTouchApp installed on your phone & InTouchApp Extension installed on Chrome or Firefox. Learn more.
How to Save all Unknown Contacts from WhatsApp Group:
Step 1 - Open web.whatsapp.com in the browser and Scan the QR code by using WhatsApp on phone.
Step 2 - Select the Contact that has shared Contact List with you - that you want to save.
Step 3 - Click on View all.
Step 4 - You will see the list of all the contacts shared by the contact. Select SAVE ALL.
Step 5 - It would show you the count of all the numbers shared, Select SAVE and all the numbers would be added to your phone contact book.