When you delete the pre-order app from your Shopify store Admin panel, you will be automatically unsubscribed from it.
To remove the app from your store:
Go to Shopify Admin > Apps
Click on Pre-Orders
Under Products, ensure all your Pre-Orders are toggled to off
Go to the app, then click on Uninstall
To confirm app deletion, click on Proceed to Uninstall
Once done, go to Shopify Admin > Apps, select Pre-Order and click on Delete
After deleting, you should not be billed. If you are still billed after deleting the app, please contact us for support.