From Lifehacker:

Whenever Attia would catch himself having a negative self talk, he would have to immediately stop whatever activity he had just messed up. Then, he would have to pretend it was actually a dear friend who had just flunked the task, and replace the self talk by audibly speaking to that person as if they were there. He would record the “conversation” on his phone and send it to his therapist.

Naturally, he would speak in a much kinder way to this friend, rather than angrily to himself. After about several months of doing this activity four or five times a day, Attia claims he can’t remember how his inner critic even sounds anymore.

The trick has to do with the brain’s ability to changing, or as he talks about in his book and is known in the scientific community, its neuroplasticity—the ability of the neural networks in the brain to change and adapt throughout an individual’s life.

While people who have a toxic inner monologue lack empathy for themselves, most still have it for other people. Ultimately, he is hacking his brain into talking to himself in a much more loving way and undoing 47 years of toxic inner monologue.