Once Office 365 Admin Enabled Multi-factor Authentication ,user will be able to create app specific password and if user wants to change the Default App Password then follow below steps,
Sign in to Office 365.
Choose Settings > Office 365.
Choose Security & Privacy > Additional security verification. You'll only see this option if your admin has set up multi-factor authentication for your organization.. If you don't see this option, contact your Office 365 admin and tell them to turn on multi-factor authentication.
Choose Update my phone numbers used for account security. This will display the following page:
At the top of the page, choose App Passwords.
Choose create to get an app password.
If prompted, type a name for your app password, and click Next.
Choose copy password to clipboard. You won't need to memorize this password.
Tip: If you create another app password, you'll be prompted to name it. For example, you might name it "Outlook."
Go to the app that you want to connect to your Office 365 account. When prompted to enter a password, paste the app password in the box.