There are thousands of people, daily, who make threats to Trump. Most are just jerks who mean nothing by it. Each one has to be evaluated accordingly to the probability of it happening.
You can report it straight to the FBI. They may have some general form that you can fill out.
“There are thousands of people, daily, who make threats to Trump. Most are just jerks who mean nothing by it.”
charge a few hundred of those putative jerks and let’s see what the rest subsequently decide to do ...
the law that makes it illegal to threaten the President with death doesn’t have a special exception that excludes “jerks who mean nothing by it” because it’s impossible to tell whether people who make such threats “really mean it” ...
in the K-12 school system in this country as it currently stands, there is ZERO tolerance for even joking around about killing fellow students and/or blowing up schools: if you’re overheard saying it or posting it on social media, you’re expelled ... period ...
exact same thing is true regarding such jokes in an airport: zero tolerance, except you’re arrested, not expelled ...
so why is the zero tolerance standard not being applied regarding the Federal law about making death threats against the President?
You can also report it to the Secret Service, use the nearest field office:
https://www.secretservice.gov/contact/field-offices