Loki migration between k8s clusters

Hi Loki team.
I’m using loki-distributed on AWS EKS, trying to test for migration between k8s clusters.
I thought that it could be done like what I attached.
But, even though throw /flush API to ingesters in old Loki, a query to new Loki doesn’t get logs that exist in old Loki.
Did I miss something?
Is there the best way to migrate between k8s clusters?
Thanks.