losing to toproll

im a beginner in arm wrestling and i have been arm wrestling for only 3-5 months. I always lose to my friend who has a strong toproll (pulling without straps) and he is more explosive so he always gets in the offensive position first when we pull. However if we do hook vs hook he can't even move my arm. I do train biceps alot. What should i do to win against an explosive toproller like him?