PIK20D vent hole machanism

Dear All,
I am refinishing my PIK20D (in-out) and I have realized that the nose
vent. mechanism. does not working. (I have recently bought this PIK,
never flown with it).
The problem is that the small circular plate which is adjustable by
the push-pull button and open-close the air flow, is separated somehow
from its normal positoion.
I am not able to figure out how it is correctly assembled,
working,...because this is not really visible at all, behind the
internal
fiberglass cockpit cover, which is not removeable.
Would anybody be so kind to help me with some hints, drawing, etc....
how to repair this nose vent ? How does it work,....?
Thanks in advance for any help