Kanwar yatra is related to the churning of the ocean of milk in the Hindu Puranas.
When the poison came out before Amrita and the world started burning from its heat then lord Shiva accepted to inhale poison.
But, after inhaling it he started suffering from negative energy of poison. In Treta Yuga Shiva's devout follower Ravana did meditation.
He brought holy water of Ganga by using kanwar and poured it on Shiva's temple in Puramahadev.
Thus releasing Shiva from the negative energy of the poison.That was the starting of Kawaad Yatra.
ॐ नमः शिवायः – Om Namah Shivaya,
Bam Bam – बम बम, Bol Bam – बोल बम, Har Har Mahadev – हर हर महादेव,
Bam Bam Bhole – बम बम भोले