Youin MA1010 Mode D'emploi page 4

How to use the adjuster
The purpose of the adjustment is to be suitable.
Turning it clockwise tightens it, otherwise it is
loosening. Please adjust it to the right.
If it is not adjusted properly, the helmet may be
misplaced or fall off when an accident occurs. the
correct operation method of the rotary regulator is
shown in the figure below.