How do I replace a negative thought with one that is a Rational ?

Not maths really is it ?

Negative thought: My hair might look a mess today and just when I have an interview.

Rational one: It looked fine when I left the house and I know should not worry so much, and anyway I can tidy it up if needed just before I go in.

The key idea is to dismiss or deal with minor worries and do not forget to smile and enjoy yourself

Change the negative thought into a thought that is rational.