Removed application

As a non-technical business owner, I am unlikely to resolve this issue myself but will rely on the development team who created the application (instance?). While everything was fine last week they noticed the application is now missing. What is the procedure to recover the application, if possible. If not we will need to recreate from backups.

Thanks for any insights or suggestions. Please be very specific on the steps needed to recover the application, or simply suggest starting over from the back up data.