Starting today you can now delete messages you sent by mistake — whether to one person or an entire group. Here's how it works: tap and hold on the message, choose "Delete," and then "Delete for everyone." You have seven minutes to delete the message after it's sent.
This feature is rolling out for users around the world on the latest versions of iPhone, Android, Windows Phone as well as desktop. Both you and the message recipient must be using the latest version of WhatsApp for the message to be successfully deleted.