Please carefully read all the replies above, actually, you're pertaining to the hard fork which was held on 2017 August.
if you were holding bitcoins when the fork was launched in august 2017, you received an equal amount of bitcoin cash to the same addresses.
To add this, you can only get those BCH if and only if you control the private keys or recovery seed of that wallet. Though most of the exchanges supported the forked coin but there are some who didn't.