Shimano FD-RX810 Dealer's Manual page 13

INSTALLATION/REMOVAL
Installing the front derailleur
3.
Adjust the position of the chain guide.
(1) Use the low adjustment bolt to align the flat portion of the chain guide outer plate
with the surface of the largest chainring.
(2) Check the adjustment position by pressing a hexagon wrench or other tool to the flat
portion of the largest chainring.
(1)
Low adjustment bolt
Largest chainring
Chain guide
(2)
13
Largest chainring