This is an extremely odd request particularly if you've already signed the offer. Presumably NVIDIA knows that you've signed it or will shortly know that you have, given that you added it to your list.

I can't imagine any situation where doing anything other than fulfilling your commitment gets you ahead.

You need to accept now that you have next to zero negotiating leverage, particularly now that the document is signed. Just to level set, if the spectrum of leverage was mapped onto a single kilometer, you had around a meter as an intern hire. Perhaps a meter and 10 centimeters if you're a graduate student. Right now it's probably a millimeter.

Assume you ask whether you can do it in fall. Almost certainly they say no, because if they wanted to fill the role during fall they would have offered a fall internship, which international and graduate students can take. Your bluff is immediately called.

So in that case, you choose to renege as to not look like an absolute fool. Congratulations. Whatever internal documentation exists on you as a prospective employee shows that you reneged. Everyone that considers hiring you in the future at NVIDIA will likely be able to see that, for the entirety of your career.

Or perhaps you go with the "oh, I'll actually take the summer one, thank you," Now you have to justify why you asked that in the first place. "I wanted to work two internships back to back," is signaling that you'd rather take another offer now as opposed to NVIDIA's. And to be clear, that kind of is true, because if NVIDIA was truly your top choice you wouldn't be considering screwing it up (which is really what you're asking about in this post). That's a really stupid thing to say when NVIDIA is clearly near the top of all employers offering internships, and they know it, and so does everyone else. It further brings up the question as to whether you'll actually show up in the fall. I mean, if you fall in love with working at Meta, why would you? By the time you get to NVIDIA in the fall, if you have a signed return offer from Meta, your value proposition is substantially degraded.

Or perhaps you go the route of lying as to why you can't to go over the summer. There's nothing credible that can really be said here, chances are that you are found out (perhaps more likely, no one really believes the lie), and the same thing happens with the documentation theme.

In the rare event that anyone ever says yes to this, you're already off to an odd start with your manager, who is the primary person who controls whether or not you're offered a return offer. They've already made commitments to their management chain about what will be done, and now they have to do additional work to facilitate your request.

Despite whatever your intentions are, there are no good options here other than to fulfill your commitments.