I didn't find where I can get SEED phrase in Bitcoin.

For now, I just dumped private key in text... what should I do next?

[...] and import the private key to supported wallet of BCH like coinomi or Electron Cash. But make sure you transfer your bitcoin first to your new wallet for security reasons and save all necessary backups offline of that new wallet.

Getting fork coins.
Here's another tutorial (by bitmover) for using coinomi wallet. Skip step 3 since you will get your private key on core (steps below), on step 4 just paste your private key on coinomi.