You don’t. Hidden Sonos signals are hidden. 
 

What signal do you think you’re trying to connect to? SonosNet, or a connection between a parent speaker and a child ‘bond’, such as surrounds or Subs?

Hi Bruce. 
I want to connect to my wifi signal from my router. 

I have a dedicated wifi signal to my sonos system. 

Your posts here are a little confusing, but note you cannot setup a Sonos sysyten with a Mac, or PC, Sonos controller App, if that is what you’re perhaps attempting to do? You must use a compatible mobile Sonos controller App to create a new Sonos system.

See these requirements…

Mobile OS Requirements:

https://support.sonos.com/en-us/article/sonos-app-requirements

Sonos System Requirements:

https://support.sonos.com/en-us/article/sonos-system-requirements
 

@Jazzbar66,

Just to perhaps cover some further things, if you have an existing Sonos system on the local WiFi network, you simply connect your new MAC to the same WiFi network and install the Sonos controller App. On opening the App for the first time, go through the opening screens and accept the T&C’s and then choose the option to connect to the ‘existing’ Sonos system on the local network - do not look to create a new system (NB: You should not see this option anyway with a MAC/PC controller App). The App will search and find the Sonos Households that are present on the same network subnet.

What exactly is hidden?

As already noted, SonosNet is hidden. Whether in ‘wired/SonosNet’ mode or ‘wireless’/WiFi mode a new Mac simply needs to be on the same IP subnet for the desktop controller to associate with the Sonos system. The Mac doesn’t have to attach to any specific SSID.

If you’re trying to connect your Sonos to a hidden SSID you may struggle a bit. There is an option down Settings/System/Network/Manage Networks/Update Networks that allows you to specify an SSID by name. It can help if the phone is also connected to the same hidden SSID, with an ‘Auto-Join’ setting. 

It sounds like you want to connect your Mac to your WiFi signal.
 

You also may have a Sonos device wired to your router which is creating a SonosNet signal for all Sonos devices to connect to. This is a separate signal that only some Sonos speakers can see, your Mac would be connected to your normal WiFi signal. 

Hi Ken. 
 

That is exacly my case. 
but the Sonos App on the Macbook would not connect to the excisting Sonos system. 
 

I have two Play One, one Move and one Playbar connected and can control them with my iPhone. 
Bit the Macbook will not connect and I have to add a music library from my NAS and to do thst, I have to use a PC, correct?

@Jazzbar66

You can use any Sonos Controller to add a NAS shared library on the local network. Just need to enter the IP address or Netbios name of the NAS and the path to the library and enter the username/password. It can be done from a mobile controller.

Anyhow, I would maybe try resetting the MAC Sonos controller App or removing/reinstalling it and ensure the MAC is connected to the correct WiFi network and not a guest network and perhaps give it another go.