Head to https://passwordreset.microsoftonline.com/ and follow the instructions.
You should've enrolled your personal email and/or mobile phone number when you first used your BDS email account. This was in order to reset your password.
To check these settings, go to https://mysignins.microsoft.com/security-info. You won't be able to do this without your password though; so if you don't know your password AND you didn't setup any personal email, mobile device, or the Microsoft Authenticator app, you'll need to submit a ticket.