Schuberth C3 Pro Adjustment

Bought a helmet for my wife after trying for several minutes the different sizes.
Large was completely loose in her head, so we chose medium.
The helmet fits tight and after about one hour on the road, we have to stop, she gets a red mark on the upper forehead.

I have heard these helmets take a while to 'break in' but would like to know if there are suggestions of what can be done to the liner... I am imagining finding a melon or a bowling bowl that would fit relatively tight and leave it for hours...

Any suggestions?

I get a "hot" spot in the middle of my forehead on all my new Shoeis. I guess I have a bump in my skull there. Anyway, I pull back the cover and push in the hard foam right in that spot to relieve pressure. I use my thumb or the back of a spoon.