I have passed my class 12 cbse board last year and I have got only73 %marks in class 12 cbse board in this year 2020 can I am eligible to take admission in btech in iiit through jeemain 2020 according to the new rules of 75%criteria

Hello,
If you are from general category, then you must have secured minimum 75% in your class 12 boards (65% for ST/SC/OBC). Apart from that if you are in the top 20 percentile of your respective boards then also you are eligible for admission into NITs IIITs and GFTIs and also eligible for JEE Advanced if you qualify in JEE mains.
As you appeared for your class 12 boards in the last year, you could have appeared for your improvement exam in the year 2020. But if you have not registered for the improvement exam, then you have no other ways to increase your score. So as you have secured only 73% in boards which is less than 75% minimum, so you won't be eligible for admission into NITs IIITs and GFTIs. Also you won't be eligible for JEE Advanced even if you qualify for JEE mains.
You can only go for private engineering colleges in India. You can work hard from there and learn new skills. After all, it depends on how hard you can work. All the best.
Here's a list of top private engineering colleges in India https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/colleges/ranking/top-private-engineering-colleges-in-India&ved=2ahUKEwjAlZHOktbqAhUTIbcAHUR4AmwQFjAPegQIBxAB&usg=AOvVaw3ZtyjIynwh5jLDs3nOHHoU

Hope it helps