You can end your subscription in the following steps:
You can delete products in the app via the import list.
Then deactivate the activated suppliers. This is possible once all products have been removed, which may take some time.
Once you have deactivated the suppliers, you can switch back to a free version.
After this, you can uninstall the app if necessary, but you can also keep the app for free and occasionally check if any new suppliers have been added.