Not sure how to do all that, which is why I posted in the newbie section. I have the public key.
Go to the website you had used it before for creating your brain wallet.
Two websites I know for creating a brain wallet are bitaddress.org and brainwallet.io. As these two websites use different algorithms, they generate different addresses and different private keys. So, note that you must use the website you had used before.
As you said you have 6 words.
Let's assume these words are Bitcoin, Ethereum, Litecoin, blockchain, wallet, Block.
You should test different combinations of these words. For example Ethereum, Litcoin, Block, Bitcoin, blockchain, wallet.
Every time you enter a combination of these words, a public key and a private key is generated by the website or the application. Continue this until the generated public key matches the public key you have. Save the private key which was associated with that public key.
Then you should import the private key into a wallet to access your bitcoins. I recommend you to use Electrum.