The Password Expiry Interval setting in System Settings can be used to set the number of days after which a user should be prompted to change their password.
To begin, navigate to Settings>System Settings>Safety & Security. 
Password Expiration Interval
Set the interval of days after which a user must update their Password. Whenever the interval passes since the last time they reset the Password, they will be prompted upon the next login to do so.
Note that you must click Save whenever you make changes to settings for them to take effect.
Learn more
- How do I change/reset an Employee username and password (web)?
- How do I change/reset my password (mobile)?