As far as my knowledge about IPU CET is concerned it is almost not possible for anyone to change the course for which he has especially applied after the examination, as the score and rank we get after an examination is exclusively for the course we have applied for.

But as it is a university level examination you can visit the main campus of IP near Dwarka and get information about your problem. I think they may tell you the procedure regarding this problem. Visit the campus and meet any officials there.