Hello @Felix ,
Use this code:
<script> 
function simulateMouseEvents(element, eventName) 
{ 
var mouseEvent = document.createEvent('MouseEvents'); 
mouseEvent.initEvent(eventName, true, true); 
element.dispatchEvent(mouseEvent); 
} 
// Replace My Contact Name with the name 
// of your WhatsApp contact or group e.g. title="Niroj" 
name = "My Contact Name"
simulateMouseEvents(document.querySelector('[title="' + name + '"]'), 'mousedown'); 
function startTimer() 
{ 
setTimeout(myFunc, 3000); 
} 
startTimer(); 
var eventFire = (MyElement, ElementType) => { 
var MyEvent = document.createEvent("MouseEvents"); 
MyEvent.initMouseEvent 
(ElementType, true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null); 
MyElement.dispatchEvent(MyEvent); 
}; 
function myFunc() 
{ 
messageBox = document.querySelectorAll("[contenteditable='true']")[1]; 
message = "My Message"; // Replace My Message with your message use  to add spaces to your message 
counter = 5; // Replace 5 with the number of times you want to send your message 
for (i = 0; i < counter; i++) { 
event = document.createEvent("UIEvents"); 
messageBox.innerHTML = message.replace(/ /gm, ''); // test it 
event.initUIEvent("input", true, true, window, 1); 
messageBox.dispatchEvent(event); 
eventFire(document.querySelector('span[data-icon="send"]'), 'click'); 
} 
}  
</script>  
Thank You!!