How can i become a medium and do like clairvoyant stuff?

Just start claiming you're one. That's what they're doing. There are millions of dollars out there for anyone who could prove that actually works, and no one ever has. If that 'psychic' were real, they wouldn't have been cold-reading you, he'd be a multi-millionaire. Sorry, but you got scammed. You can find cold-reading techniques online if you want to go scam other people.