01. create a new txt file on an USB stick
02. open the file
03. insert "options cfg80211 ieee80211_regdom=DE" (without quotes!)
04. save and close the txt file
05. rename the txt file to cfg80211.conf
06. take USB stick
07. plug USB stick into your libreelec raspi
08. Enable the "/Media/General/Show hidden files and directories" option in libreelec
09. add new source root/storage/.config/modprobe.d/
10. open modprobe.d on the left
11. open USB stick on the right
12. select cfg80211.conf on the right
13. copy cfg80211.conf to the left
14. restart libreelec
15. connect to your wifi at channel 13
16. have several beers
cheers! 
