Make mechanim slash with right arm

I have a mechanim fbx which slashes with the left arm. Now I am picking up swords in both arms, and if the sword is in left arm then it's fine. But when my mechanim picks up sword with the right arm, I want to make it slash with its right arm as well. I cannot figure it out how can I make it slash with any hand with the script.

Any help will be appreciated.

Thanks