If you're comfortable using RegEdit, try deleting:
If you get an access denied error, you'll need to right-click UserChoice, then choose Permissions, and then delete the Deny permission that may be added against your user name. It should be possible to delete it then.
The rest of this post is just an observation, and not anything you need to do, unless you see other unexpected behavior on the machine.
FWIW, there appears to be something unusual going on with your registry, where the merged HKEY_CLASSES_ROOT (HKCR) view is different to the underlying HKEY_CURRENT_USER (HKCU) and HKEY_LOCAL_MACHINE (HKLM) views:
64 HKCR.zip: "" is REG_SZ: "OpusZip"
64 HKCU\Software\Classes.zip\ -- Does not exist
64 HKLM\Software\Classes.zip: "" is REG_SZ: "7-Zip.zip"
I'm not sure how that combination is possible, since the top line should be coming from one of the other two lines (with HKCU overriding HKLM if both exist), yet it is showing something that is in neither of them. One or two other people have reported similar in the last couple of years, and I think ended up creating a new account/profile on their machines to solve it, although I would not go to those lengths unless I saw other problems with filetypes and/or the registry (which they did).
While I can't explain what the registry is showing there (unless some kind of 'cleaner' tool has been modifying the registry hives directly, perhaps), whatever is causing that unexpected behavior may also be what is preventing the usual ways of changing the .Zip association from working.