Based on my understanding of your issue description, I believe you are referring to Azure doc Quickstart: Chat with Azure OpenAI models using your own data and for the steps.
-Please ensure that the Prerequisites are met/completed, as outlined in the doc.
-Be sure that you are assigned at least the Cognitive Services Contributor role for the Azure OpenAI resource.
-Ensure that Azure App Service is RP (Resource Provider) is registered. Register the Microsoft.Web RP within the subscription settings. (as outlined in this doc)
Additionally, registering a RP configures your subscription to work with the resource provider. To register a resource provider, you must have permission to perform the /register/action operation for the resource provider.
This operation is included in the Subscription Contributor and Owner roles.*
(You may discuss with your subscription owner or admin on these points)*
Reference : Resolve errors for resource provider registration
If the issue still persists, please share a screenshot of the issue after concealing any private details, we will be happy to assist you further.