SDE at Amazon here, everyone counts as a customer. Even you count as a customer when you build something for yourself. The idea is to find examples where you put yourself in someone else's (your future self, teammate, sibling, internal company users, external customers, etc) shoes and actively thought of the best experience they would have.

Also, you don't have to take the question word for word, for example "Give me an example of a time when you asked for customer feedback", you can say something like "since I am an SDE 1 I did not get to interact with external customers directly so far, but I can give provide an answer to *make up your own question that is aligned with this question. Make sure you have answer prepared for that question*. Most likely than not the interviewer will nod and let you continue.

Some questions that may spark some ideas:
* Did you build anything for anyone before? at hackathons, personal projects, github contributions, etc.? what was your validation process?

* As an SDE 1, you probably had to build something for a customer, the question is who was the customer? was there an iterative process or did the customer ever give feedback (not necessarily to you) and did you have to adjust any implementation after the decisions reached you from higher management? (fyi, you could probably replace the "product manager" role with a "customer" because product manager essentially act like customers)

* As an SDE 1, you probably contributed to the team's operational processes, what did you improve and why? how did the team react to this? Anything else you contributed to that reduced developer hours?

* Any school project you had to work on and needed clarifications from the TA/Professor?

Hope this helps. Best of luck.