Question

Who changed vision of patol babu and how

Answer 1

Gogon Pakrashi was the mentor of Patol Babu. Patol Babu had always followed the advice of Mr. Pakrashi. He learnt from Mr. Pakrashi that even if given a small role to play, one should do it with dedication. He also learnt from him that the success of a play is the combined effort of many people.

Answer 2

The teachings of his teacher changed his vision. He remebered them when he was angry about his small role in the documentary film.
or
When Patol Babu found that his dialogue is just one word 'oh!', he felt that he had been cheated . But soon, he thought of his mentor Gogon Pakrashi and remembered his words of advice that one should not undermine any role or consider it beneath one's dignity. These words changed Patol Babu's attitude and vision toward his dialogue.