Based on ElasticSearch documentation Delete By Query API, you can delete all documents within an index using a query as following :
POST twitter/tweet/_delete_by_query
{
"query": {
"match_all": {}
}
}
With ElasticSearch Java API "Delete By Query API" documentation :
BulkByScrollResponse response =
DeleteByQueryAction.INSTANCE.newRequestBuilder(client)
.filter(QueryBuilders.matchQuery("gender", "male"))
.source("persons")
.get();
long deleted = response.getDeleted();
Please note that this answer is suitable for ElasticSearch 6.1 but may differ for other versions of ElasticSearch.
I hope this will help you.