How to recognize the 2.4 or 5 GHz WiFi?

Please keep in mind:

All WiFi routers have a 2.4 GHz band.

Newer routers are often dual-band router, with 2.4 GHz and 5 GHz bands. If both of your 2.4 GHz and 5 GHz WiFi bands have the same name (SSID) and password, you will not have any problem connecting to that SSID and add a new smart home device. 

IF there are two WiFi networks that belong to you, usually the 5 GHz WiFi band has '5'or '5G' in its name, do not connect to that one. You can also log into your WiFi router's admin page on a web browser to check the WiFi settings, such as the WiFi band name and password. You can find the login info at the back of your WiFi router or Google "router's model name admin" to find detailed instructions on Google. 

You can also check from your PC as follows: