Recently a friend gave me his used electric box that he doesn't need it anymore, so he told me to store it inside for long term and on it for long term, as it will help protect the camera / lens and keep it clean, as he saw that my lens got some mold inside and he says this will help clear it, just wanna ask is it really ok to on it for long and store my camera inside for days without taking it out ?

I believe u meant dry box?

Yes it is designed to be used 24/7. And no, most likely the mould inside your lens will not clear off, only prevents it from getting worse.

Ah yes i meant dry box, ohh i see ok so i don't have to worry about it being on 24/7 then. So my camera lens' mould will not go away but will be able to prevent it from being worse, so the only way is to clean my lens ?

U need to bring it for servicing. Reputable shops like YL and J one should offer such services.