The last step is very simple. Just add a new banner with the following details:
Header: "Chat with us in WhatsApp"
Caption (if needed): Any caption
Image: We advice you to upload
logo of WhatsApp.
Link: That you've copied before.
That's it. Now those customers, who'd like to continue conversation with you in WhatsApp will be redirected to their account and linked directly with your WhatsApp account.