How can i apply index template and ilm to existing index?

Now, i have 'test' index in elasticsearch.

Documents are written in 'test' index every day, and every seconds.

In this case, i want to apply index template to 'test' index.
For example, 'test-0000001', 'test-0000002'. and i will apply ilm policy.

How can i apply index template to existing same name index?

What is best method to apply index template?

Manage existing indices | Elasticsearch Guide [8.5] | Elastic is the best place to start there, let us know if you have any questions :slight_smile: