I'm having the same problems that many others have had migrating my NIK plugins from Photoshop CC 2017 to 2018. The plugins won't run as filters. The "Correct Answer" below is copied from another thread
Copy Google plugins folder from PS 2017 to PS 2018
If NIK selective tool is not present File>Automate>Nik Selective Tool. Selective tool should appear
Launch from Selective Tool
However there is no such tool under File>Automate. Where do I find it?
OK, I solved the problem. I downloaded and installed the Nik software from nikcollection.dxo.com. The download includes the Nik Selective Tool, which runs immediately when Photoshop is started (after you get the message from PS that the plugins are incompatible). So while I can no longer use the Nik software as plugins (under Filters -> Nik), I can launch them as stand-alone programs from the tool.
The tool can also be accessed under File-> Automate, as the "Correct Answer" correctly states.