Hi @BennyB,
I see what you mean now. I was under the assumption that you had setup a way to filter these subscribers already.
So the method to differentiate users would be to Integrate with Recharge. This would allow for your customers who have subscribed to the replenishment to be tagged so that you can section off the flow. The recharge integration allows for you to pull in custom profile properties such as the Started Subscription metric: this records an event when a customer subscribes to a product in your store using ReCharge. New subscriptions are synced in real time. After that, you could create filters that utilize this profile property. I believe recharge also has a way they utilize replenishment flows with Shopify integration as well.
Additionally, and more complex, you could use API calls such as the Track and Identify API to mark customers with a custom profile property. In the flow filter, you can also mark it so that you need this replenishment = true to pass through the replenishment flow.
Hope that made sense!
Alex