Forgot alternate Password, what to do ?

Hi,

i dont own a galaxy s5 but my buddy forgot the alternate password. and the fingerprint scanner is not working either.
can you tell me what the easiest way to get the phone working again?
we dont need any data to be backed up... it just has to work again.

root? factory reset ?
is a factory reset possible when the phone is locked via fingerprint scanner or password ?

thanks

[Q] Can't set lockscreen password after upgrading to Marshmallow

I upgraded to Marshmallow, specifically Bad Boyz Nexus Stock Rooted, and everything is working fine, but when I try to set it to something, it freezes up settings. Anyone know anything about this? Thanks.