I love the quote by Rachel Goldman, You don't want to set yourself up for failure by replacing the thought with something that may not be realistic. A helpful technique could be to ask yourself what would you say to a friend in this situation. Make sure you replace a negative thought with a realistic one. It's not helpful to replace the label, 'I'm stupid' with 'I am a genius' if you're not. A more realistic thought would be, 'I have an amazing capacity to learn when I apply myself.'