Before you proceed, you need InTouchApp installed on your phone & InTouchApp Extension installed on Chrome or Firefox. Learn more.
How to Edit Contacts from WhatsApp Web:
Step 1 - Open web.whatsapp.com in the browser and Scan the QR code by using WhatsApp on phone.
Step 2 - Select the contact whose contact information you want to edit.
Step 3 - On the top right side of the Chat screen on the Options bar, you will see a red pencil icon - Click on the same.
Step 4 - Click on the same and you would see a contact detail screen. Edit the contact you want to about the contact. Once done, click on Save Contact.
The contact detail gets automatically updated in your phone contact book.