Hi Siva Kumar,

The entrance exam for MBA in IIT is CAT(Common Admission Test).

Hope this helped resolving your query :)

Most of the IITs follow CAT score for shotlisting and then call to appear for WAT and personal Interview, with different IITs have set their own rules and cutoffs for the selection Process which varies accordingly, You can chek out whole Process of Selection to MBA in Different IITs here.

https://bschool.careers360.com/articles/mba-from-iits-know-seats-fee-and-admission-process

If you want to get into IIT for MBA program you need to give CAT(Common Admission Test)

The Common Admission Test (CAT) is a computer based test held in India. The test scores a candidate on the bases of 

1. Section 1: Verbal ability and reading comprehension- 1hour, 34 questions(102 marks).

2. Section 2: Data intrepretation and logical reasoning- 1hour, 32 questions(96 marks).

3. Section 3: Quantitative ability- 1 hour, 34 questions(102 marks).

Total no of questions will be 100 and 3 hours of time.

After giving CAT exam you will receive a call from IIT`S and NIT`S for further two rounds called GD(group discussion ) and PI(personal interview)
And to apply for it you must be completed your graduation with minimum 50% in it as this is the minimum criteria and there is no age restriction.For 2019 the last date to apply is 26th September is the last date of application through which you can get in IIT for MBA as it is conducted once a year

On the basis of which they will select you.

For more details visit official site here- https://iimcat.ac.in/

Best of luck