It's possible:
* The name is misspelled. If you could double-check the spelling, I might be able to find them.
* They are a lesser-known figure. There may be very limited information available online.
* They work behind the scenes. Perhaps they work in a role that doesn't typically get listed in credits (e.g., production assistant, costume designer).
If you have any additional information about Sydell Dowling, such as a specific project they might have worked on, their profession, or a possible timeframe, it would be helpful in finding more information.