If you’re at an accident scene and have no medical training, something you can do is collect information and help calm victims. This is quite helpful as it assists the paramedics with triage and keeps potential injured persons heart rates down. Alternatively, learn how to hold C-spine.
"People having seizures cannot swallow their tongue. Do not put anything in their mouth."
It's not that people actually swallow their tongue, it's that their tongue will rest in the back of their throats restricting their ability to breathe. People have heard this and misunderstood what was actually happening and spread misinformation for decades. So then things like this come out without actually addressing the truth or the root of the phrase. Your tongue isn't going to rip out of your mouth and go down your throat. It can rest in the back of your throat and choke you to death. That's what they are saying when they say "swallow your tongue."