I understand you are referring to this demo https://github.com/Azure-Samples/azure-search-openai-demo and that you are unable to access your application (Azure App Service Web App ) due to 'Application Error'.
You may leverage App Service diagnostics from Azure Portal> Navigate to your App Service app in the Azure Portal.
In the left navigation, click on Diagnose and solve problems
- Review - “Configuration and Management and “Availability and Performance” options.
Enable and review logs to fetch more details about the error:
Access log files
#enable-application-logging-linuxcontainer
Ref: Default-exposed-ports-of-Azure-App-Service-Linux-Blessed-Images/
Kindly let us know, I'll follow-up with you further.