Hey Gauri.

No, a student of 5 year integrated law course cannot apply for 3 year LLB programme. The reason being, that for being eligible to take admission in 5 year integrated law course you need to pass class 12th exam. Whereas for admission under a 3 year LLB course the minimum eligibility criteria is that you need to complete an undergraduate degree in any field. So as you do not fulfil the basic criteria of being a graduate for admission to 3 year law courses you can't get your course changed.

Best of luck