I ve been watching world armwrestling league events mostly the heavy weight class for the last few months and one of the top arm wrestlers is a canadian guy named Devon Larratt. The guy has an amazing endurance and strength and you can subscribe to his youtube channel and there you can find out more about his training program, techniques...
You can also watch this video of the GOAT of the arm wrestling John Brzenk and try to imitate his workout techniques.
Here is the list of the competitors of the WAL? click on any competitor to read his biography, learn more about his table IQ, power... Then just google the name and look for his workouts.