I got it. So first of all your need to get your data from reddit. Through that, you can get every id for your posts and comments, and then you write a script that loops through each id and edits then deletes. It’ll take a while depending on how much data you have.

Here’s the script my friend wrote for me (which works better than the one I wrote):

const zzz = ms => new Promise(res => setTimeout(res, ms));
(async () => {
  let uh = document.querySelector("input[name=uh]").value
  for (const id of ids) {
    console.log(id)
    await zzz(3000)
    await fetch("https://www.reddit.com/api/editusertext", {
      method: "post",
      headers: {
        "content-type": "application/x-www-form-urlencoded; charset=utf-8",
      },
      body: new URLSearchParams({
        thing_id: `t1_${id}`,
        text: Math.floor(Math.random() * parseInt("fuckspezfuckspezfuckspezfuckspezfuckspezfuckspezfuckspezfuckspezfuckspez", 36)).toString(36),
        uh,
      }).toString()
    })
    await zzz(1000)
    await fetch("https://www.reddit.com/api/del", {
      method: "post",
      headers: {
        "content-type": "application/x-www-form-urlencoded; charset=utf-8",
      },
      body: new URLSearchParams({
        id: `t1_${id}`,
        uh,
      }).toString()
    })
  }
})()

You will need to run it with the old reddit layout so that it can fetch the CSRF token.