Yes you are eligible to appear for JEE main 2019 because eligibility criteria does not require 75% in class 12th it is required when you are going to take admission to IIT NIT GFTI.

• There is no percentage criteria to appear for JEE MAIN.
• For candidates belonging to OBC general category and wish to take admission into IIT or NIT they need to score at least 75 percentage or need to be within the top 20 percentile of the board.
• For candidates belong to SC ST category the need to have at least 65 percentage in class 12th to take admission into NIT or IIT or have in the top 20 percentile of the board.

Without75 percentage you can appear for JEE main and take admission into colleges which does not have any criteria on class 12th marks many private colleges in many other state colleges also offer admission based on the JEE main marks and does not have any criteria on class 12th percentage there for you can take admission into The scholars is also there are many opportunities for you in the private colleges if you can afford because many colleges does not have any criteria on percentage in class 12th so you can go for those colleges by appearing in to entrance exam  and take  admission into them