Hello aspirant, 

To get seat for NITs,IIITs or GFTIs through CSAB Special Round the first criteria is that one should be JEE Main qualified as per his/her category. Now for once  category, the 2019 JEE Main cutoff was 79.75 percentile. So if you have cleared the required cutoff then you are JEE Main qualified and hence eligible for CSAB Special Round counselling. Now with a rank of 68k, it can be hard for you to get a seat in IIIT through CSAB especially since you are a old  category candidate. Better apply for the counselling process and whether do you get your choice of college or not. 

You can go through this link and checkout the detailed information regarding CSAB Special Round counselling : https://engineering.careers360.com/articles/csab

Good Luck !