Being from arts background will not hinder your selection in IIM's but IIM's focus on past academic records, CAT percentile and then other selection rounds like GD/PI and WAT.

So lets assume for top 3 IIM's like IIM A, IIM B and IIMC.

Check the selection process below:

IIM A

IIM B

IIM C

You can check how much you will get rated as per your past academic records out of 10. This may vary IIM's to IIM's.

You will be required to score a percentile above 99 to get into top colleges because you have an average past academics.

Hope this helps.