You have a central place of awareness within from where you have the capacity to observe your thoughts and perceive all those different parts of you, including the Inner Critic.
And being in that aware space, you can consciously SEPARATE from that part, in this case the Inner Critic. Separating doesn't mean pushing it away. Rather, acknowledging its presence, its perspective, even its attempt at helping you out (each part of us always has a function in our lives, albeit their methods are often misguided), and realising that YOU are separate from it.
The second thing to remember is that:
YOUR THOUGHTS AREN'T THE TRUTH. And therefore, you don't have to believe everything you think.
What a radical viewpoint, ha! When I first heard this it really put so many things in a different light, a much more empowering light.
So how to use this practically to tame your Inner Critic is:
Really listen to your thoughts, so you can spot them when they come. Too often we're not even aware of our thoughts and yet they totally influence how we feel and act.