It works the same way as inoculation delivered in a syringe.
You give your audience a small dose of the opposition's argument to stimulate their defences.
How to use innoculation as a persuasive technique
Let's take it step-by-step.
1. Present your case.
2. Warn them of an attack - preferably with a weak example. Maybe: 'You'll hear some people say that the world must be flat because thousands of people disappear each year. They must be falling off the edge.'
3. Encourage them to reject the attack. It's especially effective if they come up with the ideas. You can ask them how they would reply.