You really havent given us a lot to go on.
If you are talking about Mac, go to the Chrome site and look for their previous downloads section and you should find old builds in there.
If you are talking about an iPhone, you can't. The version in the App Store is the one you get when you install it. I'm sure a dodgy repo could give you an older version for a jailbroken device if you searched Google hard enough but I wouldn't recommend it just for an older version.
For reference, it's much easier for us to provide you with meaningful and targeted assistance if you can provide as much information up front.
Just putting one word in the text field is unhelpful and i'm sure you wouldn't want the responder to be equally as lazy now, would you?