Use the ‘Administration’ -> ‘Commands’ feature to run the LED controls commands.
LED Control on my R7000 (build 39960M) was successful with the following commands:
# Disable four LAN LEDs
et robowr 0x0 0x18 0x1ff
et robowr 0x0 0x18 0x0
et robowr 0x0 0x1a 0x0
# disable WPS button LED
gpio disable 14
# disable WLAN button LED
gpio disable 15
gpio disable 16
# turn off 2.4GHz LED
gpio enable 13
# turn off 5GHz LED
gpio enable 12
# turn off power LED white
gpio enable 2
read also this related article on the DD-WRT Forum
R7000 LED Control