Every you have two attempts for JEE Mains first of that will be held in the month of January and the second attempt will be in the month of April. You are entitled to appear in any one of them or Both of them, and your best score will be counted among them.

This both attempt will be in the same year that is if you are interested in taking admission in a college in 2019 then attempt in January 2019 and April 2019 will be counted in them there is Nothing to do with the JEE Main January 2020.

If you appear in April 2019 then this will be counted as a part of JEE Main 2019. And if you appear in January 2020 then it will be Counted in JEE Main 2020.