from the wiki on ways to conteract genjutsu
The ninja needs to stop the flow of chakra in their body, and then apply an even stronger power to disrupt the flow of the caster's chakra; this is called Genjutsu Dissipation (幻術解, Genjutsu Kai). This can also be done by an unaffected ninja by applying a sudden surge of chakra into the affected person.[7] In addition, tailed beasts can break their jinchūriki out of genjutsu in a similar fashion if they have a good enough cooperation, as seen in Killer B's case
So basically this means that the person under it just has to stop and disrupt their chakra flow like when Kabuto used that sleeping genjustu and kakashi released it by disrupting his chakra its not the point that the byakugan has a power to block genjutsu
its that its lets you sense it better and gives you great chakra control thats gives you a good chance at stopping it