HowtoAddMoreDatainIndexinElasticsearchthatisalreadydefinedusingOlivere

I can insert the data into elasticsearch using olivere, but if I want to add more data into existing index that has been created before, it won't work.

This is the code

package main

import (
    "context"
    "fmt"
    "strconv"

    "github.com/olivere/elastic"
)

type Tweet struct {
    User    string `json:"user"`
    Message string `json:"message"`
}

func main() {

    client, err := elastic.NewClient(elastic.SetURL("http://localhost:9200"))
    if err != nil {
        fmt.Println("%v", err)
    }

    n := 0

    for i := 0; i < 1000; i++ {

        bulkRequest := client.Bulk()
        for j := 0; j < 10000; j++ {

            n++
            tweet := Tweet{User: "Markus", Message: "This is the new from string representations of basic data types. " + strconv.Itoa(n)}
            req :=
                elastic.NewBulkIndexRequest().Index("twitwar").Type("tweet").Id(strconv.Itoa(n)).Doc(tweet)
            bulkRequest.Add(req)

        }

        bulkResponse, err := bulkRequest.Do(context.Background())
        if err != nil {
            fmt.Println(err)
        }
        if bulkResponse != nil {
            fmt.Println("Data have been inserted", i)
        }

        fmt.Println("I", i)

    }

}

How can I add more data into index that has been defined before?

Thanks