The application for registration of an establishment employing migrant workers in Bihar, under the Inter-State Migrant Workmen (Regulation of Employment and Conditions of Service) Act, 1979, is submitted using Form I (as per Rule 3(1)). This form requires details about the establishment, the principal employer, contractors (if any), and the migrant workers employed. The application, in triplicate, must be submitted to the Registering Officer of the area where the establishment is located.