1. Visit the official website of the University of Mumbai.
2. Click on the 'Online Services' tab.
3. Select the 'Marksheets' option.
4. Click on the 'Lost Marksheet' link.
5. Enter the required details such as your name, roll number, college, and year of examination.
6. Pay the required fee.
7. Your duplicate marksheet will be generated and you can download it from the university website.
Note: It is important to note that you may need to contact your college or the university directly for further assistance in obtaining a duplicate marksheet.