I did it from terminal as stated here https://forum.gl-inet.com/t/gl-mt300n-v2-unable-to-be-repeater-for-wifi-network-channel-13/10743 for the GL-MT GL-MT300N-V2.
Not sure if that works for other routers.
@alzhao is there a similar way for other routers?
uci set wireless.mt7628.country=‘DE’
uci set wireless.mt7628.region=‘1’
uci commit wireless
wifi