I would recommend you to search the syllabus in the official website of the board or just search in Google search you will get a plenty of options from where you can download hindi syllabus.

For more details regarding syllabus rather than Hindi , follow the link provided below from career360.com (//career360.com) :

https://school.careers360.com/articles/bihar-board-12th-syllabus

I hope my answer helps you. All the very best for your future endeavors!