Based on my understanding, you are using the Microsoft Purview service to connect to and manage the ChatGPT Enterprise app for auditing, please correct me if I'm mistaken.
If the ChatGPT Enterprise app was previously registered and scanned using Microsoft Purview, you may still be able to retrieve relevant audit and access information even after deletion. Here are a few ways you can proceed:
Scan History in Purview
Navigate to Microsoft Purview > Data Map > Sources.
Locate the ChatGPT Enterprise data source (it may appear inactive).
Review the scan history for insights into what data assets were scanned, classified, or labeled.
For additional information, please refer: Monitor scan runs
Lineage Tracking
Go to Purview > Data Lineage.
Search for assets that were connected to the ChatGPT Enterprise app.
Lineage diagrams may still show upstream or downstream data interactions the app had.
For more details, please refer: Data lineage in Microsoft Purview
Purview Insights
Under Purview Insights > Scan Insights or Asset Insights, filter for the relevant time period before deletion.
This will help you identify which assets were accessed or categorized by the app.
For more details, please refer: Understand the classic assets report in Unified Catalog
If Logging Wasn't Enabled
If the app was deleted before enabling Microsoft Purview scans, audit logging (via Microsoft Entra ID), or external logging tools (e.g., Azure Log Analytics or Microsoft 365 audit logs), and if it cannot be restored, there may be limited or no access to historical activity.
I hope this information helps. Please do let us know if you have any further queries.
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Thank you.