How do I get rid of a "hidden network". ? Don't know how it became hidden.

What kind of “hidden network” do you refer? If this is a WiFi “hidden network”, you must change the WiFi settings of your WiFi Router.

Recommended settings for Wi-Fi routers and access points - Apple Support

Your WiFi Router is hiding the network; you must change the WiFi settings of your WiFi Router.

To do so, you will need to use your browser to access the management page of the Router. You will need to consult your Router manual - or if your router was provided by your Internet Service Provider (ISP), you may need to find the appropriate documentation through their technical support pages.

Recommended settings for your router can be found here:

Recommended settings for Wi-Fi routers and access points - Apple Support

If the same WiFi network is visible to other devices, this would suggest an issue with the iPad itself. Try a reset of Network Settings:

Settings > General > Transfer or Reset iPad > Reset > Reset Network Settings

No.

A hidden network attempts to hide the network name that is broadcast by the WiFi Router - making casual network discovery more difficult. Ironically, for technical reasons beyond the scope of this post, this feature actually weakens security - and engenders a false sense of security. The network name can be easily discovered using readily available network tools.

A Private Wi-Fi Address - a privacy feature - replaces the “real” MAC Address (a hardware address, assigned during manufacture, that is truly unique) of the device with a fake MAC address. Using this feature makes tracking of device by it otherwise fixed and unique hardware address significantly more difficult.

Can you post a screenshot (if necessary, redact the image to remove any personal information)?

Take a screenshot on your iPad - Apple Support

There should be a “Hidden network” choice if you scroll down.

To repeat an earlier comment, the hidden network setting will be found in your WiFi Router settings - not iPad settings.