How to request a channel avatar in telegram?

Question

Telegram

there is a certain channel whose data is received via getChat for the bot API. The following data is coming

{
  "ok": true,
  "result": {
    "id": -some_id,
    "title": "some_title,
    "type": "group",
    "all_members_are_administrators": true,
    "photo": {
      "small_file_id": "AQADAgATSgOcDgAEBM8B5kE2JQXNHwQAAQI",
      "big_file_id": "AQADAgATSgOcDgAE0WQLVY44V7vPHwQAAQI"
    }
  }
}

As you can see there is a nested photo object which contains photo IDs. You need to download one of them. I don't understand how this can be done. I did not find any API for this or I was looking in the wrong place