Debug an external dll called by a custom action called from an updatable BAQ

Hi

I am looking for any instructions\guides or pointers in debugging code that was written for us but we now need to fix. My problem is how to debug the code in visual studio. I understand the code and have access to the source code but really need to step through to identify where exactly the problem is. For some reason adding simple things like writing to log file within the code do not appear to work.

any help appreciated

Open Visual Studio
Enable debugging
Import the source code as new a. dll project
Find the errors in debugging mode errors list
Resolve the errors
Save as. dll
Replace existing. dll with saved one