But I found one discussion but I have no idea if this will really help https://www.reddit.com/r/Bitcoin/comments/19xzpt/how_can_i_use_the_blockchaininfo_walletaesjson/
"How can I use the blockchain.info 'wallet.aes.json' file to get my funds into my local wallet?" < the user already has his wallet.aes.json file and only wants to decrypt it, which is the easy part.
Have you read this op post clearly. He mentioned way of decrypting wallet with the .json file. It has been given the steps like we see in FAQ page. Since he is not clearly does not understand it. He asked again with the forum members.
I have used the blockchain but more 6 months ago. I did not find the option in the setting page at all. If clearly explains with the perfect steps, example Wallet ---> Setting---> accounts---> QRcode to pair the device on mobile. This above one is example to pairing the device on android. Same like that how to use the json file?