How to generate recovery phrase from private key I created a brain wallet with a non standard phrase.

So I have that, the private and public keys.

Now this wallet app wants a 12 word recovery phrase to set up the wallet.

How can I convert what I have into a 12-word phrase that it can use?
Firstly, it is highly recommended not to use a brainwallet, your coins will be stolen.

But in general, if you have a private key, there is no way to obtain the 12 word recovery phrase from it. That is because the 12 word phrase is used as a seed to generate a hierarchical deterministic master extended private key, as described in BIP 39 and BIP 32 and this process is not reversible. Also, your private key is not an extended private key which is needed for an HD wallet, so the best you can do is simply import that single address manually. Some wallets do not support importing of individual addresses for safety, because they wouldn't be covered by the 12 word mnemonic backup. So I would suggest just generating a new wallet and everything and forgetting about your brain wallet.