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mining is replaced by witnesses, a witness signs a block just like a miner would do, but to be a witness you have to be voted in . so the witnesses (miners) are delegated by the majority of steemians voting for them.

So, how to become a witness? Do you have any idea?

Yes. I am a witness. I can point you in the right direction.
I will get back to you with some information.
Feel free to contact me in chat :-)