Also you need to be using the otg cable to change it to 2.4ghz.
Take a look on YouTube and type in search bar dji spark 5.8 to 2.4 change.
It slid bring up lots of video's showing how to do this procedure
Spark supports 2.4 GHz/5.8 GHz operating frequency. Like hallmark007 mentioned, when you select a channel, it will pop up a message: It will reset Wi-Fi and take effect.