How rotate a flange in Inventor?

Hy guys , could you show me how can I rotate a flange in assembly Inventor 2018?
I need rotate by an axis just18 degrees.
See print screen for more informations.
Cheers
Accepted answer

as far as I can see on your picture you constraint both flanges with an angle constraint with one of them 18.8 degree and the other one with 161.8 degree which is 180degree minus your 18.8 degree and flipped the second flange so the holes of both flanges arre aligned.
Just set one of this two angle constraints to 0 degree