You'll need to do these steps once.
Open Outlook, such as Outlook 2010, 2013, or 2016.
Wherever you're prompted for your password, paste the app password in the box. For example, if you've already added your account to Outlook, when prompted paste the app password here:
Or, if you're adding your Office 365 account to Outlook, enter your app password here:
Restart Outlook.