HKPR Thanks for posting your question in Microsoft Q&A. I assume you have setup an API to call Azure Function App and would like to redirect to App Service URL in Azure API Management. Is that correct?
You can use return-response
policy to perform the redirection of requests by setting status code (based on your need: Redirection messages) and location header and here is the doc reference: Return Response. We have similar discussion in other thread and sharing code snippet for reference:
<inbound>
<return-response>
<set-status code="303" reason="Redirecting" />
<set-header name="Location" exists-action="override">
<value>@("https://app-service-url/")</value>
</set-header>
</return-response>
<base />
</inbound>
I hope this helps with your question and let me know if you have any other.