You can access the Modify Results tab from the detail page:
To access your modified endpoint, append the parameter
&kimmodify=1 to your API call to apply your function to your results.
Let's say I have API with API ID: zkvisgr9
To call this API without the modify function, your call looks like this:
Now, to apply the modify function to the endpoint, the call looks like this:
If you want to use a kimparameter and a modify results function at the same time, you can do that as well! For example, if you want to include the source urls for a crawl, you could call your api like this: