The very basic thing that you can do to fix pretty much everything is a simple reboot of the phone. If for some reason the screen is frozen, just hold down the volume down and power button until the screen goes black. Once the screen is black, let go and your phone will boot up by its self.
If the restart didn’t fix the problem, you should try and booting into safe mode. Sometimes a simple app can get in a conflict with another service and prohibit its function. Booting into safe mode disables all third-party apps and only runs the necessary things from the operating system.
If the fingerprint scanner works in safe mode, next thing you should do is restart the device, let it boot into normal mode and start diagnosing what app makes the problem. You can uninstall apps one by one (first the one that have something to do with the phone sensors), and after each one try the scanner. The stock apps that come with the operating system cannot be uninstalled, so just disable them.
If the problem continues to appear, you should consider resetting the phone to its factory settings. But, before you do this you need to back up your data. Factory reset WILL erase everything.
Reset Galaxy S7 to Fix Fingerprint Sensor Problem
Factory reset Galaxy S7 or S7 edge the easy way
- Open the Settings
- Choose Backup & Restore > Factory Data Reset.
- Now select Reset Device> Erase Everything.
- Confirm the warnings and wait for the process to finish.
- Once done, reboot your phone.
Hard reset Galaxy S7 or S7 edge using recovery mode
- Power off your device.
- Wait for a few seconds while your phone is shutting down.
- Press and hold the Power, Volume Upand Home buttons simultaneously to get into Recovery mode. Use Volume keys to navigate and Power button to select an option in Recovery mode.
- Once in, from the main menu, using Power key, select wipe data factory reset.
- If you want to clear app data cache too, choose wipe cache partition. Clearing cache often fixes various software related issues.
- When done, go back to main recovery menu.
- Select reboot system now and that’s about it.
If the problem persists after the factory reset, you should get your phone to an official Samsung service to test the scanner itself.