Hii..

The marks of both session of JEE main that in January and April are not going to be add..

It's totally your call whether you are going for both exam i.e for January session  and also for April session or whether you are going one of only one of them the best thing with going for both is that if your score will less in one then there will another chance so.. you will improve your marks in second one..

For more information about GM in go through this link:

https://engineering.careers360.com/articles/jee-main-exam-pattern/amp

All the best!!