There are different ways to say thank you in Hindi.
A simple thank you is धन्यवाद (dhanya-vaad) in Hindi.
If you wish to say thank you very much, you’ll say ” बहुत बहुत धन्यवाद (bahut bahut dhanya vaad). Now बहुत (bahut) means “many” in Hindi.
So “बहुत बहुत धन्यवाद (bahut bahut dhanya vaad)” is many many thanks.
The one more way to say thanks in Hindi is to say “शुक्रिया (shukriyaa)” . Now “शुक्रिया” is a Urdu word though it is regularly used in day to day conversations.