How to reindex data in Elasticsearch without actually changing index names?

Elastic Stack Elasticsearch
7

I am using Logstash to push data to ES index. Configuration of Logstash would be something like,

output {
                elasticsearch {
                        hosts => ["host1","host2","host3"]
                        index => "project-%{+YYYY.MM}"
                }
}

Can you please say where would this month's data go if I delete project-2017.10(after reindexing data to project-2017.10-1)?