Use wifi direct at 2.4GHz on Galaxy Tab S2 I would like to configure my Galaxy Tab S2 to use the 2.4GHz frequency for WiFi direct because my PC doesn't support the 5GHz band. 
I'm using Total commander with the WiFi plugin to create a WebDAV server to be able to see the files on the tablet on the PC. This plugin can work by connecting to a wifi network but you can also use a wifi direct connection. My laptop is mostly in a room without a wifi connection, so  I would like to use the wifi direct option. However, it seems that this tablet only creates a 5Ghz wifi connection with WiFi direct.
Is it possible to configure it to use the 2.4Ghz band? How?
It is strange that you are trying to use wi-fi direct to accomplish this task. AFAIK most Wi-Fi Direct compatible devices use the 2.4GHz connection  (by default) and given that most devices nowadays only communicate with other Wi-Fi Direct-certified devices not just random.

I suggest you simply use a standard wi-fi connection i.e something like a mobile hotspot using your device or PC as host. If it is a case that your mobile predominantly uses 5GHz connection, then you can use this to force a 2GHz connection.

Another option apart from WebDAV server is using an SMB, FTP server or even TCP server of your folder structure in sdcard or internal storage similar to this.