Update event specs containing existing app ids (#1002)

Author: DianaIgnatescu

docs/understanding-tracking-design/defining-the-data-to-collect-with-data-poducts/index.md

@@ -27,8 +27,8 @@ With data products, you can:
 - **Event specifications**
     * **Name;** a descriptive name for the event 
     * **Description;** a description to help people understand what action the event is capturing
-    * **Applications;** the application/s that the event will be tracked on
-    * ** Triggers;** specific instructions on where the event gets triggered (e.g. when a user clicks the "Add to basket" button)
+    * **Source Applications;** the source application(s) inherited from the data product containing the Application ID(s) that will be sent with this event
+    * **Triggers;** specific instructions on where the event gets triggered (e.g. when a user clicks the "Add to basket" button)
     * **Event data structure;** the event data structure that this event will validate against as it is processed by your pipeline
     * **Entities;** the entities that should be attached to this event (e.g. user, product)
     * **Properties;** any specific rules for each property of the event

docs/understanding-tracking-design/defining-the-data-to-collect-with-data-poducts/ui/images/edit-existing-data-product.png

@@ -46,4 +46,14 @@ In the image below, you can see an example of a data product. It not only provid
 
 ![Event specification details](images/event-specification-details.png)
 
-If you need to edit a data product at any time, simply select it from the data products listing accessible from the main menu.
+If you need to edit a data product at any time, simply select it from the data products listing accessible from the main menu.
+
+#### Updating existing Data Products following the release of Source Applications
+
+Data Products created prior to the release of [Source Applications](../../organize-data-sources-with-source-applications/index.md) in September 2024 will need to be updated to assign Source Applications in which the events will be tracked on. The selected Source Applications will add the relevant application IDs to each of the event specifications in the data product. 
+
+![Updating existing Data Products](images/edit-existing-data-product.png)
+
+Event specifications which contain previously added application IDs will need to be updated to use the identifiers inherited from the Source Applications selected at Data Product level. This process can be done manually but you can reach out to our Support team to help you with that by either logging a request through our Snowplow [BDP Console](https://console.snowplowanalytics.com/) or by directly emailing [support@snowplow.io](mailto:support@snowplow.io).
+
+![Updating existing Event Specifications](images/edit-existing-event-specification.png)