Damet garm means to have "warm breath" or be alive. Mehdi Akhavan Sales (OMID) used this expression in poetry, specifically in "Zemestan," when he said "damet garm o saret khosh bad." It is good for your dam (breath) to be garm (warm) because it means that you are alive. It is used as an expression of gratitude.
Hey samad agha Damet garm for doing that