When you use a dropshipping app, suppliers are usually notified automatically as that is part of the dropshipping process. You can learn more about how dropshipping works through our Ultimate Guide to Dropshipping. It will walk you through everything you need to know about starting off, finding suppliers, and maintaining your business.
If you're not using an app, could you tell me a little more about your business model and how you're expecting to use Eprolo or cj dropshipping?
The better I can understand your store setup, the better I can help you!