You might want to update documents already indexed, for example if you your service name was set incorrectly.

For this you can use the Update By Query API.

Rename a service

To rename a service send the following request:

POST /apm-*/_update_by_query
{
  "query": {
    "term": {
      "context.service.name": {
        "value": "old-service-name"
      }
    }
  },
  "script": {
    "source": "ctx._source.context.service.name = 'new-service-name'",
    "lang": "painless"
  }
}

Remember to also change the service name in the APM agent configuration accordingly.