PGPM Eligibility

Yes, you are eligible!
PGPM: Admission Process
Aspirants with least 50% marks in Graduation (under the 10+2+3 plan) from a recognised university are exempted from the entrance test for admission. Interested applicants with beneath 50% marks in graduation are required to pass in the test (MAT/CAT/XAT/ATMA/some other state-level test). To be qualified for the interview. There will be no cut off score. Interested applicants, if not passed in any specified test and with less than 50% marks in graduation, are required to appear in the Aptitude test to be conducted by AIMA/Study centers. They might be given provisional admission with a commitment that they will appear in the Aptitude Test whenever finalised.

Well, it's good that you have a clear goal right from the start. I'll keep the answer short and list out a few things you should keep in mind to get admitted in one of the good IIMs.
1. First, make sure you do well in your studies during engineering. Your overall performance during your bachelors degree has a huge weightage. So, make sure you keep that up. While colleges often have their requirements listed out as 60%, make sure that you maintain your score at least above 75%.
2. Prepare for CAT: You might already know that to get admitted to one of the IIMs, you have to clear your CAT exam. Start preparing for this exam right now. Often people take a gap year after engineering to clear the exam. While there is no harm in it, don't prefer it. Instead, start preparing for the exam right now. If you want to take a gap year, take up a job during that year. That will get you extra points.
3. Prepare for your interview: I can't stress on this enough. Work on your soft skills while you have the time. Only 30% of the people who clear their CAT exam actually make it to a college. So don't ignore the preparations for your interview.
4. Do some short term courses: Depending on the field of MBA you want to get into, you can take up some short term courses. When you go in for admission interviews, you will be required to make a resume. Now that resume should have some weight. Apart from your participation in college fests, organizations, and academics, courses can get you some serious weightage. Plus, they'll grab the interviewer's attention and give your interview a direction that you can be prepared for.

Hello,
It is indeed very nice to hear from you that you are interested in doing a postgraduate Masters program in management from one of the IIM's after completion of your graduation in engineering. I am attaching a link which will give you all the required information about the generic criterias applied by IIM's to give admission based on the common entrance exam called CAT. However every IIM has its different nuances. IIM Ahmedabad is famous for declaring that it wants a wide variety of backgrounds of students to join the class and hence if a student has a very typical background, even with low score one can get admission and on the other hand some students with 100 percentile also have been rejected.
https://www-shiksha-com.cdn.ampproject.org/v/s/www.shiksha.com/mba/articles/amp/iim-eligibility-blogId-15091?amp_js_v=a2&_gsa=1&usqp=mq331AQCCAE=#referrer=https://www.google.com&_tf=From %1$s&share=https://www.shiksha.com/mba/articles/iim-eligibility-blogId-15091
Best wishes to you.