JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
 <html>
 <head>
 </head>
 <body>
 <p><iframe src="//www.youtube.com/embed/rk7_dXIKt0Y?start=1" width="560" height="315" frameborder="0" allowfullscreen="allowfullscreen"  allow="autoplay"></iframe></p>
 </body>
 </html>

JavaScript

// RegEx Source:  https://stackoverflow.com/a/37704433/362536
const youtubeUrlPattern = /^((?:https?:)?\/\/)?((?:www|m)\.)?((?:youtube\.com|youtu.be))(\/(?:[\w\-]+\?v=|embed\/|v\/)?)([\w\-]+)(\S+)?$/;

[...document.querySelectorAll('iframe')].filter((iframeEl) => {
  // Filter to iframes loading YouTube URLs only.
	return iframeEl.src.match(youtubeUrlPattern);
}).forEach((iframeEl) => {
  const a = document.createElement('a');
  a.href = iframeEl.src;
  a.search = a.search || '?';
  a.search += '&autoplay=1&mute=1';
  iframeEl.src = a.href;
});