He cancels the first date because he's anxious: what to say back

People rarely cancel a first date over nerves unless they care how it goes. Someone who's indifferent usually just says they're busy, or stops replying. Naming the anxiety is a sign he's trying to be honest rather than slippery, and that counts for something. Read it as: he wanted this enough to feel pressure about it.

The question to answer is whether the anxiety is about you specifically or about first dates in general. If he's mentioned past dates going badly, or he tends to over-prepare and second-guess, it's probably the generic kind, and it will fade once he's sat across from someone. If he's said things like "I don't want to disappoint you," he's already imagining you as someone to impress, which is more likely to make the next attempt harder unless you lower the stakes.

Before you propose a new plan, make the plan smaller. A coffee or a walk is far easier to agree to than dinner, and a shorter meeting gives him an exit that doesn't feel like failure. You're not asking him to stop being nervous, you're making the thing he's nervous about less ceremonial.

You also want to avoid reassuring him so heavily that it becomes a task. A line that tells him you're not expecting anything dramatic lands better than a speech about how it's fine to be nervous. Keep the reply light enough that he can answer it while still feeling a bit of it.

Answer the same day or the next morning. A long delay after a cancellation reads as you being hurt or losing interest, and it gives his anxiety more room to talk him out of trying again. A quick, warm reply tells him the door is open without you having to chase.

If he doesn't respond to a rescheduling offer within about three days, send one short follow-up that's easy to answer, something like a specific time you're free. If that also goes unanswered, stop. Someone who will only engage with his own anxiety and never with a plan has told you what the next few weeks look like.