Correcting an error in the program in C#

There's source code. A C# program with a base in SQLite. It's not starting. We tried to correct it, said that there were 3 classes and several performances missing, but I unfortunately don’t understand anything about it, and the person stopped contacting at the last minute. You need to fix it as soon as possible to make it work. There are screens of what it should look like, a verbal description of what it should do.