It depends on your browser. For example, Chrome chooses the default cam (in this case, if you use a laptop, it’s likely that it will be used automatically), while in Firefox you can choose which cam to use. In Chrome, you can also choose usb camera - but you have to set it for the whole browser.
If you have any additional questions about Interviews or would like to leave your feedback, please reach out to your Customer Success Manager or contact us at support@codility.com.