You can rectify it during the month of January 2018 on the jee mains website when cbse will provide a link on jee mains website for correction. You can edit all your particulars except the mode of examination and language of exam paper.

Dear Sharma
The correction in particulars can be done only if the
candidates have paid the fee and completed all the steps of online application form of JEE (Main)  2018. Thecandidates can modify all the particulars including city of examination, Paper - 2 to Paper -1 and vice versa or select both papers of his/her application form during the facility of correction in January, 2018. The balance fee, if any due to correction in particulars, will have to be paid by the candidates during that period. However change of mode of examination from
computer based to pen paper based examination is not allowed.
And also you can edit that In the month of January.
Now,  they haven't tell the exact date.. Please go through the JEE mains official website for the exact date.
All the best.

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