Every State and UT releases the NTSE application form separately. The last date to apply also varies from state to state. Since you haven't mentioned your state, you can click on the link below to know if the application form in your state has been released. You will have to submit the form offline after getting it attested by the principal of your school.
you will get it from your school as the NTSE exams are conducted and the school is able to send their students for giving this exam by filling up the forms by their portal so ask to your teachers about this exam.
JEE Main College Predictor
Know you Admission Chances for NIT and Other B.Tech College based in JEE Main Score