You need to contact the developer of this "firstclass" app and obtain from them instructions for installing/using it on your specific BB device model and OS level. If they have not written their app for BB10, then it's not available...but they remain your resource regarding if/when it shall ever be.
Occam's Razor nearly always applies when troubleshooting technology issues!
If anyone has been helpful to you, please show your appreciation by clicking the button inside of their post. Please click here and read, along with the threads to which it links, for helpful information to guide you as you proceed. I always recommend that you treat your BlackBerry like any other computing device, including using a regular backup schedule...click here for an article with instructions.