Here's how you can apply for an emergency appointment for US student visa

1

You will have to pay the application fee

2

Then you will have to fill up the Nonimmigrant Visa Electronic Application that is DS-160 form.

3

You will have to pick an appointment date online. You will see a message onscreen showing available appointment dates including emergency appointments. 

4

You will have fill an Emergency Request Form and give an authentic reason for applying for the same.

5

You will have fill an Emergency Request Form and give an authentic reason for applying for the same.

6

You will get an email from the US Embassy if your request has been approved.