There are two ways to handle this, generally speaking:
Look online. If you don’t read or write Chinese, this will be difficult for you and you might need the help of a Chinese friend or girlfriend. Try searching for 成都租房 on Baidu to get started.
Hit the street in that area and visit some rental agencies. It can be a hassle but there’s almost no way to find a good apartment in Chengdu without a considerable amount of leg work.