Make a joke to your crush to lighten the mood.
Laughter often goes a long way in soothing anger. This also allows you to gauge the response so you can verify if your crush seems annoyed or not.
Ask if your crush is upset.
If you know why your crush is angry, mention the specific issue so you can get a more detailed response. Listen to the answer and don't assume that you know how the conversation will go.
Apologize for your actions if they contributed to your crush's being angry.
Explain your perceptions and what your intent was. This helps create empathy that can lead to forgiveness as your crush understands your point of view.
Ask how you can make it up to your crush.
This should be playful to try to reestablish a friendly interaction. This also gives you the chance to suggest a date or another situation where you can interact with your crush in a positive way.