There are two ways I know of to easily solve this problem. The first way is have your program request a debugger attach to it as the first thing it does in Main via Debugger.Launch()
public static void Main(string[] args)
{
Debugger.Launch();
//Rest of your code here
}
This will make a dialog like the following show up
This will allow you to attach to your running visual studio or start a new instance.
The other way to solve this when you can't use the previous method (for example I don't think it works inside services) is put a loop at the start of your code that will loop forever until a debugger is attached, this gives you enough time to do the "Attach to process" method you tried earlier without letting the program progress.
public static void Main(string[] args)
{
while(!Debugger.IsAttached)
{
Thread.Sleep(1000); //Sleep 1 second and then check again.
}
//Rest of your code here
}