How to get code back from my last install?

I had created an install of my application, then later a task was given to add to this application

The Task was to check if users had access to the sqlconnection if they didnt display a nice message so to test this i contacted the dba and he removed me from the list and the task worked but for some reason when i created a new installer package the code got jacked up messing up my application, however the previous installer works, so is there any way for me to derive the code from the previous setup.exe file??? it would be amazing if i can get the code back because now i regained access to my database.

Appreciate any suggestions in advance!!!