Primark Retail assistent interview questions

The first question was to give an example of when I delivered good customer experience, an example of when I was under pressure and had to get other people to help me (something like that), tell me about a role/position you've held where you have had to speak to people face to face and communicate with them clearly, tell me about a time where you've had to quality check your work to make sure it was up to a good standard. She told me I would hear back within 10 days or sooner, and the next day I received an email saying I passed the interview.

How would you deal with an upset customer?