No problem! You need to send an HTTP Request from your application (the one whose Client ID you provide in the request header).
For testing, you could use Postman to send the request manually, refer to their docs to learn how.
Otherwise, for sending requests from the application itself, refer to the documentation for any HTTP Client API which you’ll use in your application. For example, in JavaScript, you might use XHR, Fetch, or a library like Axios. Within those docs, look for info related to “sending requests” and “setting request headers”.