Hi Sophie,
Unfortunately the big problem with brand new devices like yours is that sites like iFixit haven't had a chance to get one in hand and create all the guides people want for it, plus the aftermarket vendors haven't had the time to design and build parts for it.
The Pixel Fold is unique and Samsung is the only one currently making that foldable screen, so it's unlikely you're going to find anything but genuine Google replacement screens for some time to come.
Google officially uses UBreakIFix as their repair service and you can supposedly get a quote for having the screen replaced on their site.
Google Pixel Fold Inner Screen Repair
They also make parts for their phones available through iFixit, but it doesn't appear that iFixit has gotten any screens for the Fold yet. You can always ask them by emailing their Store personnel at support@ifixit.com. I don't see anyone else selling a replacement online yet.
The closest I see for a guide would be the video teardown done here by iFixit, but hopefully that will get done soon since there seem to be a lot of people reporting issues with the inner screen already.
iFixit's Google Pixel Fold Teardown
For now I'd suggest that your best bet would be to use the UBreakIFix service, given the lack of availability of the phone and the dearth of instructions for doing the replacement. I realize this is the antithesis of what this site is all about, but sometimes you just gotta be practical when the resources aren't there for you to be able to do it yourself.
Good luck, and let us know how it all turns out with your phone!
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