Migrate Elasticsearch from Elastic Helm Charts to Elastic Operator (ECK)

I'm migrating our stack from the Elastic Helm Charts to Elastic Operator (ECK). Are there any easy guides/recipes for migrating without losing all my data?

Thx.

If u have a paid license I think cross cluster replication would work.

While I'm in the process of migrating everything to Elastic Cloud, this is specifically for our current on-prem instance with a Basic License, so cross-cluster won't work in this case.