These commands don't work on my Raspberry Pi 3B+ 
iw reg set "YOUR-COUNTRY-CODE"
iw reg get
Can someone help me and explain in detail how to operate the solution provided by the official Wiki?
Thank you very much, everyone.
Original page link: [OpenWrt Wiki] Raspberry Pi
Wireless Country Code
Setting the Country Code under Network → Wireless in LuCI does not work with the Raspberry Pi, you will need to set the country code in the latest Raspberry Pi OS. Then you can go back to OpenWrt where the new country code will be used. Starting with Raspberry Pi 3 B+, the on-board WiFi won't even start if there is no country code.