After it fails a couple of times, you should get the option to sign in with your Google account. Apparently, this might not work if you have 2-step Verification enabled. You will need to log in to your Google account on another device in order to turn it off. You will find it under My Account> Register & Security. Once you are out, go into the details of your S7 and you should be able to unlock the phone.
If you have registered and remember the details, then head to Samsung Find My Mobile website. You can use the Unblock my function screen to gain access.
You could reset your S7 factory, but this will completely eliminate all the data on the phone, so it is really the last resort. If you wish to do so, then start by turning the S7 off. Now press and hold the Power, Home, and Volume up buttons at a time until you see the pet on Android screen. Use Volume Down to highlight Data Erase / Factory Reset and Power Button to select it. Choose reboot the system now when done and put your S7 from scratch.
Possible solutions:
Before you try the solutions, it's worth holding down the Power button for ten seconds to get the Galaxy S7 to reboot. Test the fingerprint scanner again when the S7 is turned back on.
Clean the scanner with a clean cloth.
Try to press firmly and, if that does not work, try to press very lightly.
If you configure it without a case on your S7, and then put a case in, it could be affecting the scanner. Try not to include it and see if it makes a difference.
If you do manage to access, then go to Settings> Screen and lock security> Fingerprints and make sure you add new fingerprints and eliminate the old problems. Make sure that you move your finger around to cover different angles when you are adding new fingerprints and using the four slots to maximize your chances of working.