Hi,
See this thread : V3 - Selective Tool disappearing .
Note that the Selective Tool panel will not open unless you have opened an image. So, in this case, you are unable to access the Selective Tool panel settings.
The new implementation of the Selective Tool is disturbing, to say the least. It doesn’t behave like any other PS panel although it should. This issue has not been answered until now but IMHO, I think it’s now time to fix it.
To make the Selective Tool panel re-appear, use the File | Automate | Nik Selective Tool menu. This will not fix the “hide and seek” problem, though.
Also, with version 3.3, I had to install twice before the Selective be visible. The first time, the “host applications” dialog box of the installer was merely empty. No host application had been recognized.