Go to settings and on the general tab you should see a bitcoin cash option there. Please be informed that if you didn't have any bitcoins stored there before the august fork, that option will not be available to you. Its strange though because if you've checked your email they sent their announcement with a short instructions regarding this.
So you mean to say all those newly created wallets won't be able to exchange because there is no option?? I just create a blockchain wallet recently.
Yes. I can confirm there is no option for bitcoin cash on people who didn't have bitcoins there at the time of the fork because that also goes for me. This is because blockchain.info are only allowing limited support on bitcoin cash it means they do not fully support it and actually, It shouldn't be considered a BCH wallet in the first place. If you want a true BCH wallet you can go to their official site for a list of wallets.
I just found this on blockchain.info
Please note: if you did not have any bitcoin/BCH in your wallet at the time of fork then this option will not be available. The Blockchain.info wallet is not a true BCH wallet. We are only making these funds available within our wallet to users who had bitcoin/BCH at the time of the fork.