Enter password instead of fingerprint recognition after restart

[Derrick Dowuona]

I have a Samsung Galaxy Note 5. I recently(and accidentally) updated from Lollipop to Marshmallow. My battery died one day and when I turned it on, it asked me to enter a password instead of fingerprint(which I normally use). My problem is that I have forgotten the password I used, and now I have no way of unlocking the device. I even tried Android Device Manager to change password but it didn't work. Please I need to know how to unlock my phone without having to delete everything on it