Before proceeding, you can take a self-troubleshoot for the FIFINE K668 microphone. Please include the test result when requesting email support via web@fifine.cc.
Is "USB PnP Audio Device"/"FIFINE K668 Microphone" seen by your Windows or Mac, or is it recognized as an unknown device?
If it's recognized, what you want to do is to hear the mic play through your computer speaker?
If the computer sees it as an unknown device, have you tested out on a different computer? Tried to update and reinstall the unknown driver a few times on the same computer?