Hi Marjon,
The only way you can find a username for mSecure is if you have been using mSecure 5, which is the latest version of the app. If you were using mSecure 4 for mobile or mSecure 3 for desktop, there is no username, because there was no account system in that app.
Are you trying to upgrade to mSecure 5 by chance? If so, are you able to access your information in the older mSecure app on any of your devices?
Marjon