How to change the unix timestamp to the format like "YYYY-MM-DD HH:mm:ss"

Elastic Stack Elasticsearch
1

Hi, I update the time field from unix timestamp format to "YYYY-MM-DD HH:mm:ss" format in the kibana settings, but it is not work, and there is not any error logs. when to discover, there is not result found. After i change mapping "begin_time": {
"type": "date",
"format": "yyyy-MM-dd HH:mm:ss"
}
,always not work.
I use es version 2.1,kibana version 4.3.1