You talk to a lawyer and do what they say, not what Apple demands of you. No one but a judge can demand anything of you.
At this point, the assumption would be that they are a non-party witness.
So, beyond not destroying any potential evidence, you might as well tell them to shove it.
The lawyers told us ahead of time we'd be getting the letters. They told us what we needed to preserve and what we could comfortably trash. There was never any follow-up or specific requests for what I had on my machines. That was that.
The idea that getting a legal request is scary is silly. We were employees getting employee guidance from our employer on what to do at every step of the way. We weren't individuals fending for ourselves, wondering about getting something wrong, being taken in for questioning. We were doing what we always do, work hard and listen to the company lawyers if they have something to say.