Post ingest, how can I generate lat long fields into geo point

Thank you. After a little fixing around, here is what I came up with.

1. After initial ingest, I create mapping of soon to be created "coordinates" field

PUT /my-index/_mapping
{
  "properties": {
    "coordinates": {
      "type": "geo_point"
    }
  }
}

2. Run script to generate new "coordinates" field

POST my-index/_update_by_query
{
  "script": {
    "inline": "ctx._source.coordinates = [ctx._source.lon, ctx._source.lat]",
    "lang": "painless"
  },
  "query": {
    "match_all": {}
  }
}

I changed the inline field to be in brackets because I kept getting errors of the "," between the lon and lat fields. Also I changed the order to lon,lat because that's how in the documentation it said to order it

3. Open up Maps and find your index available to start mapping!