Just contact Itch support (support@itch.io), tell them the game you'd like refunded and why, and wait for the process described previously to play out.
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No problem. And correct, you'd have to buy again. I mean, the download is a file on your system, I can't really control that. But if we're working on the honor system yes, you'd delete and re-buy when/if interested.
I may not come back to this threat to remind you, but you should get an email from Itch once it's gone through the whole system confirming the game has been refunded. And again, brace yourself for a wait, it's whenever Itch gets around to answering emails, twice. So could be three or four days, could be a couple weeks. I'll try to keep a close eye on my email so I can respond promptly though.