If I passed class 12 in 2018 but percentage is less than 75 then I do class 12 from nios and attempt jee advance 1 time then can I give jee advance 2020

You can apply for good private universities or institutes who are taking their own entrance exam and having their own admission criteria like:

SHIVNADAR UNIVERSITY

NORTHCAP UNIVERSITY

MANIPAL INSTITUTE OF TECHNOLOGY

BENNETT UNIVERSITY

IILM UNIVERSITY,GURUGRAM

LOVELY PROFESSIONAL UNIVERSITY

BML MUNJAL UNIVERSITY

AMITY UNIVERSITY

SRM UNIVERSITY etc

You can also try for state level counselling for engineering admission.

IILM UNIVERSITY,GURUGRAM is offering B.tech in computer Science and Information Technology with contemporary computing areas like:

Cloud Computing

Artificial Intelligence (AI)

Big data

Internet of Things (IoT)

Machine Learning

Deep Learning

Image processing

Block Chain

First you can focus on the jee  mains study's .
The percentage criteria for the admission in IITs is 75% must. For the without reservation students ,if you are belong to reservation caste then you don't require the 75% in 12th because reservation category student require upto / more than 65% in 12th.
Best of luck for your future.
Thank you.