No, there's no need to repeat your board examination if you want to repeat JEE examination. You can give jee examination for three times. JEE examination will be conducted twice in a year and you are eligible to write twice in a year. Best marks among 2 examinations will be considered as your marks. Let's say you want to write JEE in 2021, you should have passed your 12th atleast in 2019 and not before that. Read this article for more information in JEE Mains 2021: https://engineering.careers360.com/articles/jee-main-eligibility-criteria