I don't think you can reduce a 5 shards index to 2 shards. You would need to reindex instead in a new index.
But you can reduce to 1 shard I think. Here is a typical script to do that on an index
INDEX in a cluster which has a node with name
# Read only and move primaries to one single node and no replica
# Check shards allocation
# Shrink the index
Check the fluentd documentation. May be you need to change an index template...
BTW did you look at Cloud by Elastic, also available if needed from AWS Marketplace, Azure Marketplace and Google Cloud Marketplace?
Cloud by elastic is one way to have access to all features, all managed by us. Think about what is there yet like Security, Monitoring, Reporting, SQL, Canvas, Maps UI, Alerting and built-in solutions named Observability, Security, Enterprise Search and what is coming next ...