Copy the snippet below as a bookmarklet in order to use it:
javascript:(function(){var a=prompt("> WhatsApp Message Bridge <\nAutomatically send messages from one chat to other.\nEnter with the source and destination chat names separating those with one vertical bar (|).");if(a){var c=a.split("|")[0].trim(),d=a.split("|")[1].trim(),a=Store.Chat.models.find(function(a){return a.name===c}),b=Store.Chat.models.find(function(a){return a.name===d});if(a&&b)a.msgs.on("add",function(a){b.sendMessage(a.body)});else alert("One or more of the chats were not found. Try again.")}})();void 0;