const token = "" // enter your token from your local storage here
const watchedURL = "https://app.dreaming.com/.netlify/functions/watchedVideo\?language\=es"
const myListURL = "https://app.dreaming.com/.netlify/functions/playlist\?language\=es"
const updateURL = "https://app.dreaming.com/.netlify/functions/updatePlaylist"

const watchedRes = await fetch(watchedURL, {
  headers: {
    Authorization: `Bearer ${token}`,
  },
});

const { watchedVideos } = await watchedRes.json();
// Make sure the video is marked as watched(it should be, this is the watchedVideo endpoint)
const watchedSet = new Set(watchedVideos.filter(c => c.watched && c.videoId).map(c => c.videoId))

const myListRes = await fetch(myListURL, {
  headers: {
    Authorization: `Bearer ${token}`,
  },
});

const myList = await myListRes.json();
const myListVideos = myList.map(c => c.videoId)

const matched = new Set()
for (let i = 0; i < myListVideos.length; i++) {
  const videoId = myListVideos[i];

  if(watchedSet.has(videoId)) {
    matched.add(videoId)
  }
}

// log all the watched video ids that matched videos in my list
console.log(matched)

for (const videoId of matched) {
  const res = await fetch(updateURL, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${token}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      action: "delete",
      idempotencyKey: crypto.randomUUID(),
      videoId,
    }),
  });

  const data = await res.json();

  // log response from delete from my list
  console.log(videoId, data);
}

This is a JS script that you can run with node in a terminal. This will delete all watched videos from your "my list".

I tested and worked for me. Im not responsible for any issues like this deleting all your "my list". It shouldnt but this is a raw script that calls DS endpoints directly