Once you install the app, it will immediately start syncing all your past orders and current inventory from your Shopify store.

You don't have to do anything manually! It all happens automatically right after you install the app. You might have to wait for up to an hour if you have a lot of orders & products.

To see latest inventory in the Forecast report, press button shown in following screenshot. Refresh the page after 5 min to see the latest values in the Inventory column and updated Reorder quantity based on the latest inventory.