How to reset alternate password on my Sansung Galaxy tab s2?

[AC Question]

I can access my device using fingerprint or a simple swipe on the screen. However, whenever i try to change my security settings, a demand for a password pops up and unfortunately i can't remember my alternate password. i tried to reset the device using "lock my device" on google device manager, but the security settings didn't change at all. My tablet still asks for the old password. How do you solve this? The software is updated to marshmallow 6.0.1 version.