In Crystal, Suicune learns Bite at level 1, unfortunately since when you encounter Suicune at Tin Tower it's level 40. Bite (which Suicune learns at level 1) is replaced with Gust which it learns at level 31. Gust replaces Bite because Bite is the first move Suicune learns and Gust is the fifth, and so to make room for gust, the game makes Suicune forget Bite.
If you want a different move on Suicune instead, here is a list of moves Suicune can learn in Generation 2. (Gold, Silver and Crystal)
Hope I helped :)