45fa users: how to use the horseman reflex finder support wire?

hi everyone,

finally I have found and bought the reflex finder by horseman.
I have attached it and it's great. The one thing I am not sure about though, is the metal support wire.
It is supposed to prevent the finder from be shaky, but where to attach it to?
maybe there are horseman 45fa users that can explain?

THANKS!