Hello Chandan Kumar,First of if you did 12th in 2018 and given improvement in 2019, then you are eligible to give JEE Main 2018,2019,2020 and JEE Advanced 2018 and 2019 only.You can't give JEE Advanced this year.
And According to your certificate you have to mention 2018 as passing year and 2019 as improvement year in Application form.
So if you filled 2019 as passing year then you have to correct it as it will create problem during counselling time now,but now the correction Window for JEE Main April has been closed, it was opened from 12/03/2020 to 16/03/2020.
But don't worry as the Admit for JEE Main has not been issued till now, so you can mail about your issue to JEE Main official email id given on the website or you can call on the number given on the website.

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