Hi guys,
Thanx @Eniqmatic
I've done this job with the following config:
 mutate {
    add_field => { "realtimestamp" => "%{@timestamp}" }
        }
      ruby {
        code => "event.set('logstash_processed_at', Time.now());"
        }
    mutate {
    convert => { "logstash_processed_at" => "string" }
        }
    date {
    match => [ "logstash_processed_at", "ISO8601" ]
    target => "@timestamp"
    add_tag => "timestamp_changed"
    }