https://www.youtube.com/watch?v=ofSPk795C9w
https://faq.whatsapp.com/general/account-and-profile/about-changing-phones/?lang=fb
https://www.quora.com/I-changed-my-phone-and-installed-WhatsApp-on-my-new-phone-with-the-old-SIM-card-Since-I-removed-the-SIM-card-on-my-old-phone-I-can-no-longer-access-or-see-my-old-chats-because-it-asks-for-verification-Is-there-any-way-I-can-access-the-chats-on-my-old-phone
Built-in app -> https://www.lifewire.com/android-marshmallows-file-manager-121661