FIrst edit your A chart to not include the resource, and add the keep annontation
https://helm.sh/docs/howto/charts_tips_and_tricks/#tell-helm-not-to-uninstall-a-resource

annotations:
    "helm.sh/resource-policy": keep

From this point, your resource is not managed by helm anymore
Clean the resource (annotations...)

Then import the resource so it's managed by B chart
https://jacky-jiang.medium.com/import-existing-resources-in-helm-3-e27db11fd467

Pour obtenir les yaml sans installer un helm chart :

helm template \
--values ./values/prometheus.yaml \
--output-dir ./manifests \
./charts/prometheus