I do a lot of volunteering work that involves helping people who are having difficult psychedelic experiences. You can't actively try to calm someone like that down; as you said, it doesn't work. The better thing to do is just to be there to hold space and act as a "reality anchor." Mild reassurance can be helpful if the person wants it (especially the reassurance that the state is temporary), but inexperienced people usually try to "guide" the trip, which basically never works.