Format triggered_time to local time zone in action

try this (note that this example fully overwrites the payload, you may want to add this to the additional payload instead)

POST _xpack/watcher/watch/_execute
{
  "watch": {
    "trigger": {
      "schedule": {
        "interval": "10s"
      }
    },
    "input": {
      "simple": {}
    },
    "actions": {
      "log_error": {
        "transform": {
          "script": """
return [ 'date': Instant.ofEpochMilli(ctx.trigger.triggered_time.getMillis()).atZone(ZoneId.of("Europe/Copenhagen")) ]"""
        },
        "logging": {
          "text": "Triggered time (UTC):{{ctx.trigger.triggered_time}}  - Triggered time (Europe/Copenhagen):  {{ctx.payload.date}}"
        }
      }
    }
  }
}