How do students ask for leave to go to the bank to do business?

Just explain the situation directly.

For example: Teacher, I want to take a leave and go to the bank to do something. Go when there is no class, so you can get things done without delaying your studies.

Ask for leave, a Chinese word, pronounced qǐng jià, which means to ask the teacher for permission to take a leave due to business or illness. The explanation refers to requesting permission to take leave due to business or illness. Source: Liu Yiqing of the Southern Song Dynasty, "Shi Shuo Xin Yu Pai Tiao": Gu Changkang served as the assistant of Yin Jingzhou, and asked for leave to return to the East.