Applying ILM for backing indices of Elastic Integrations' datastreams

Elastic Stack Elasticsearch
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Hello everyone, I am trying to apply the ILM for the backing indices of Elastic Integrations' datastreams. I see that we have a separate built-in Lifecycle of datastream to set the retention of data.
The problem is I want to keep the hot-warm-cold architect, the steps I did is

  1. Create a new ILM ( I do not know how we should config the alias here for the rollover)
  2. Update the index template of that datastream to use the ILM
  3. Apply the ILM to the existing backing indices
    I am quite a newbie and afraid of some conflicts in the mapping. So do you guys have any clear docs or already did this before? I just switch to use the new Elastic Agent and fleet integration and datastreams.
    Thanks in advance.