The iPhone 7 has an all electronic button. There is no physical actuator anymore so both the "click" and TouchID functions are embedded in the electronics of the Home Button Flex. So while you can purchase a replacement button, it will not do anything but "fill the hole".
If the problem with the HB is the click function (TouchID still works), then that can be repaired via a micro-soldering repair. If the problem is lack of TouchID, then the only way to repair it is to bring the iPhone into an Apple store for a screen/button replacement.