Please please - remember they need you far more than you need them and your confidence will grow as you learn more skills and meet more lovely people.
Try not to view the interview as a pass or fail but use it to be curious about them and for them to know some more about your background, likes and dislikes. They probably just want to make sure you are real - Be brave, if you use this as a training get to know them style chat - not an interrogation. Often there are no right or wrong answers only what you can do to fill in the gaps about you beyond your name and age.
The training you receive - learning first aid skills and training for your First Aid at Work are life long skills and I think you will really enjoy the courses and the skills. You can always do this first if you want to, and apply again when your confidence has improved. But if you can find the courage to do the interview again (which I know you have done), climb back in the saddle and you will probably find you learn more about yourself in the process and realise you have more courage than you know. This alone is a real positive and you might use it in future job interviews as a difficulty you recognised and constructively managed.