Lately I've edited some credit pages on IMDB, correcting and adding stuff, but lately these updates hardly have been updated when I next look. One example being on the Finding Dory page where I put Nemo's New Voice Actor, but it's not showing up.
How long ago did you submit it? Submissions can take a week or even more.
According to the Data Processing Times page, Filmography: Cast (non-TV) credits have only been fully processed to 24 August 2015, so if you submitted after this date, it may still be awaiting processing.