How do I connect my Altek-Lansing InAir 5000 to Wi-Fi and find its IP address?

Here is the manual on the Internet Archive page, as it appears to no longer be available from the manufacturer:

https://archive.org/details/manualzilla-id-7410115/mode/2up

There are quite a few steps that they require for manual setup by first connecting to the devices own Wifi network and navigating to the configuration page of the device at http://192.168.1.12. It is there that you choose your private Wifi for the device to connect. Apparently they used to have an app that made setup easier, but not sure if they still make it available in the App Store.

When you are setting it up after pressing the WiFi setup on the speaker, you log into a WiFi network broadcast from the speaker where the IP Address is known by the manufacturer for your speaker, and it is not one being provided by your router. That will bring you to the configuration page of the speaker. After you choose your WiFi network on that configuration page, then the speakers will be assigned an IP Address from your router, just like it does for any other device.

The speaker won't have an IP address unless it's connected to the network or your connect to the speaker from your computer or device when its placed in setup mode. Your Router is what assigns the IP address to the speaker.

You can set up the speaker on Wi-Fi, by pressing the button on the speaker. Then looking for it in your computer or device's Wi-Fi settings as a Wi-Fi network and connect to the speaker.

Once connected, open a web browser and navigate to https://192.168.1.12 to access the speaker's web interface to setup Wi-Fi.

https://www.manualslib.com/manual/693586/Altec-Inair-Ma5000.html?page=13#manual

When you set the speaker to setup mode it acts like its own router, and gives itself that IP so you can access its web interface while connected to its own Wi-Fi network.

Once setup is completed and its connected to Wi-Fi it will get whatever IP your router assigns it, not 192.168.1.12.