>Hi everybody,
>
>I have a DLL project. To the main class (based on the public interface) I added a property called lTraining.
>
>That dll is being invoked as a service (my colleague added that service).
>
>My question is - how can we somehow pass 'Training' parameter (may be to that service) and how would it then set that flag property?
>
>Thanks a lot in advance.

Do you mean that you want to start the service with a parameter or that you want to change the flag whilst the service is running ?
If the former that then might help: https://stackoverflow.com/questions/42812333/pass-an-argument-to-a-windows-service-at-automatic-startup

If the latter then you have lots of options: named pipe, web sockets, WCF etc......