Hello velusamy ,thanks for asking this question on this platform.as you know from 2019 JEE will be conducted by National testing agency twice in one year and any student can appear for either in any one phase or in both phases so if you attempt or give exam in January still then you can easily give exam again in April .thanks 

Hey.

For JEE Mains 2019, you can attempt both the January as well as the April session or you can attempt either one of these. So, you attempt the April Session of JEE mains even if you have already taken the January exams.  The best out of the two exams will be considered for admission purposes.

Best of luck