BTW I am using Blockchain wallet.
Again, someone right me if I'm wrong please
I am not sure if he is talking about Blockchain.com or Blockchain.info 
Blockchain.com seems like Coinbase, it's not really a wallet, users can't own private keys
If Blockchain.info, it's easy to follow:
Quote
1) Save and run the standalone tool attached to this article.
2) Enter your seed (12 words or more) at the "BIP39 Mnemonic" box.
3) Select the original coin (the parent of the fork) from the dropdown list of coins.
4) Scroll down to the list of addresses. Each address has an accompanying public and private keys.
5) You can get the private key directly by text, or by going with the cursor the key, the page will show the qrcode.
This content is excerpted from the article in my link above2) Enter your seed (12 words or more) at the "BIP39 Mnemonic" box.
3) Select the original coin (the parent of the fork) from the dropdown list of coins.
4) Scroll down to the list of addresses. Each address has an accompanying public and private keys.
5) You can get the private key directly by text, or by going with the cursor the key, the page will show the qrcode.