There is no issue with applying with the old id with which you have appeared in the jee January attempt . All you have to do is log in with the same credentials you have logged in for January attempt and this time apply for April attempt. There is no issue with that thing. If you have applied as a fresh candidate that also does cause you any troubles

Hi Yash.

NO. You will get a new application id after you fill your appllication form this time for the April's JEE Mains 2020. You will have to fill that new application form id in your registeration form for April's attempt even if you have applied as a fresh candidate.