[Updated]
This should do the trick
You can try this simple selector. Assuming that the src is at the beginning
let URL = `<iframe src="https://player.vimeo.com/video/33535353" width="650" height="375" frameborder="0" allow="autoplay; fullscreen" allowfullscreen></iframe>`;
let updatedURLArr = URL.match(/"(.*?)"/)
var updatedURL = updatedURLArr[1].replace('https://player.vimeo.com/video','https://vimeo.com');
console.log(updatedURL)
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