Strategy Object Manager does not have the ability to migrate subscriptions from one environment to another.
This is a known limitation of Object Manager. The subscriptions in the metadata are stored in in the link item table. Currently it is not possible to change the project ID for multiple subscription objects.
The only way to migrate subscriptions is with project duplication.
Currently this issue is still being reviewed for feasibility by our Technology team and it is not scoped for any upcoming scheduled Strategy release.