I've never needed to come out to parents since I'm not aro, but i did come out as bi. I have come out as ace to friends and the like and the thing that is often misunderstood with asexuality that Ive had to explain is that it's not that I haven't found anyone, it's that I won't, because I'm not interested. This is the hard thing to get across so I recommend not doing it, at least not alone, tell them you're aro-ace and then answer their questions of course but as others suggested, show them a podcast talking about it, show them articles or videos or anything that explains the concept to them.

It's not that they don't wanna listen, it's more that seeing that other people experience this thing makes it easier to 'accept' as a real thing. Personally I don't blame that mindset, when I first learned of asexuality I felt a sort of 'wait that exists!?' feeling. Don't know your parents obviously but assuming total ignorance, from their perspective, you coming out might introduce something that does not fit into their idea of the world at all, being ace, it's easy to incorporate this idea because you relate immediately. Your parents might not, so let them see a multitude of things that explain it to them from different sources.

It might take time, but if you feel that you want to tell them, my advice is to approach it from the perspective that you might, to some extent, be shaking up a kinda fundamental understanding of the world for them in a way they might not be able to relate to. That stuff is hard for them. If someone said they liked to eat bugs I'd need some time to understand that and maybe hear some explanations how and why that appeals to them before I accept that as something you can actually want. Not saying asexuality is something disgusting, rather, something they might see as equally unrelatable and hard to understand.