Responding To Polytheistic Greetings Or Blessings
If he was referring to the name same as we say “God” in english or “Khuda” in urdu or “Bhagwan” in Hindi, then you can respond with a proper Amen and a thank you. If they are using a proper polytheistic name then just say ok and move on. If the situation allows then you can also use this opportunity to do a little dawah by telling them about monotheism in Islam. But this depends on the assessment of your situation.