I accidentally aggroed Boyn Venim during the Redoran Horator quest. Now he just attacks me not allowing me to challenge him to the duel. Unfortunately, my nearest saved game is days earlier.

Is there a console command to reset his aggro? I looked on the wiki but didn't notice one that would do it.

stopcombat might work. Alternatively, add the stage of the quest where he challenges you to a duel. The ID is B5_VenimHort and the value is 30. After entering this command walk or coc to "Vivec, Arena Pit" and defeat him in combat. Make sure to only loot one item from him or you could further impede the quest.

Wouldn't the Calm Humanoid spell work?