Python MongoDB Update array element at index

Question

So I've been struggling with this problem for a while now and this is my last resort.

I need to be able to access and update a specific element in an array. I don't know the index in advance.

def SetTask(self, taskIndex, taskInfo):
        todo = self.client.db.todo.update_one(
            {"_id":self.user["Info"]["todo"]},
            {
                "$set":{
                    "tasks":to_dict(taskInfo)
                }
            }
            )

I don't know how to access the element so any help would be appreciated.

A little help with how I've structured my database:

I have 2 different collections, one storing the user information and the other storing the to do lists for each user. Separated in case the document size limit becomes a problem later on as originally, it was going to be a sub document of the user document.

What I am basically doing here is finding the to do document that corresponds with the user, then trying to update the element at the index given as a parameter.

{
  "_id": {
    "$oid": "616865fae96df36467a89629"
  },
  "tasks": [
    {
      "basicInfo": "Basic",
      "furtherInfo": "Further",
      "dateDue": {
        "$date": "2021-10-14T17:25:27.831Z"
      },
      "event": "event1",
      "completed": false
    },
    {
      "basicInfo": "Basic",
      "furtherInfo": "Further",
      "dateDue": {
        "$date": "2021-10-14T17:29:18.901Z"
      },
      "event": "event2",
      "completed": false
    }
  ]
}