Where is the Network Diagnostics - Assist panel in High Sierra ?

where is the network diagnostics/Assist panel in High Sierra ?

For some years now, following an OSX update, the WiFi functionality became unstable; I would often HAVE to use the Network Diagnostics to get WiFi working again. Now that option is gone.

In Yosemite it was accessed like this:

- Network Preferences

- Assist Me

- Diagnostics

- Continue through steps...

and here is the Network Panel in High Sierra; the "Assist Me" button at bottom is gone! I have searched for diagnostics but haven't found.

In High Sierra I still get hang-ups in WiFi, and usually have to wait an indefinite amount of time, reset my router, or restart the Mac.

thanks