Hey this is straight from the USCIS:
Optional Practical Training Extension for STEM Students (STEM OPT)
On March 11, 2016, the Department of Homeland Security publishedallowing certain F-1 students who receive science, technology, engineering, and mathematics (STEM) degrees, and who meet other specified requirements, to apply for a 24-month extension of their post-completion OPT. The 24-month extension will replace the 17-month STEM OPT extension previously available to STEM students (see73 FR 18944). Eligible students may now apply for a 24-month STEM OPT extension.
Applying for a STEM OPT Extension
To apply for an extension, you must properly file:
- Form I-765 with the application fee on or after May 10, 2016,
- Form I-20, Certificate of Eligibility for Nonimmigrant Student Status, endorsed by your DSO on or after May 10, 2016, and
- A copy of your STEM degree.
If you file your extension application on time and your OPT period expires while your extension application is pending, USCIS will extend your employment authorization for 180 days.
Note: If you are currently participating in STEM OPT based on a 17-month extension or you have a pending application for a 17-month STEM OPT extension, please see thesection below for more information.
If you want some assistance from an attorney then feel free to try. Our site has a bunch of experienced immigration attorneys who have assisted international students with their visa applications.