How to update field inside nested document?

[Magnus_Kessler]

Have a look at scripted updates in the Update API.

POST tmp_test/doc/1/_update
{
  "script": {
    "lang": "painless",
    "source": "ctx._source.LineItem[0].CONumber = params.CONumber",
    "params": {
      "CONumber": "9876"
    }
  }
}