Raw? With utensils or just chomping away?
You can eat your own skin from your hand.
The flesh too, but you’ll need to consider any medical needs this creates, and the ridiculous costs of health care assuming you’re in the USA.
If you’re just talking about the eating, and not the amputation, then I think that as long as your hand is off and you’ve got the flesh and aren’t in the custody of a hospital (maybe you were just lying by some train tracks and lost it but they kept it on ice for you till you recovered), then I don’t expect there is any law against making a rare dish of it.
As for wanting to have someone remove major body parts, there are people who do want that, and documentaries I have seen about them and their run-ins with the medical and psychiatric establishment. Turns out it’s a bit tricky to find doctors who want to oblige such requests, and there are those would would want to diagnose them as having “body dismorphic disorder” (the feeling that you’d like not to have some body parts) and try to stop you and treat you instead. I imagine it’s a red flag for health insurance providers. But I don’t think it’s illegal per se, unless someone deems you might kill yourself, as in many jurisdictions suicide is criminalized.
Here’s a wiki-page on self-cannibalism which implies it is only illegal if you force someone else to do it,, as has been done, though apparently in the name of governments, as a part of war and conquest and such “noble” causes.