Hii Prajwal!
Usually, UPSC exams are held based on all over subject knowledge. It is the exam containing general knowledge about all the subjects possible, whether it is arts, commerce or science subjects. Usually class 10th onwards syllabus is included, so you must read everything. Thus, it can't be said in particular that class 6th syllabus is there. Study everything you can including general knowledge and current affairs. You can refer the following link for more information -
https://www.upsc.gov.in/
Hope this helps.
Good luck!