To use Skype for Business for Android or iOS, you need a Skype for Business account—typically the same user name and password you use when signing in at work or school. If you're already using the desktop version of Skype for Business, then you have a Skype for Business account.
How do I reset my password?
First you need to find out whether you can change your own password or if your school or organization takes care of password resets. How do you know? Go to the Microsoft Online Password Reset tool and follow the instructions.
If self-service password reset is available in your organization, you'll be able to follow the on-screen prompts to change your password.
If it's not enabled, the tool will send a new password request on your behalf to your workplace technical support—typically the person who set up your Office 365 account for you.