Good day to you //sue!
Is there any difference between the paired dives at all? Are they assigned to a different computer, a different diver, a different air tank, a different certification? If there are any consistent differences between the pairs you could filter your dive list based on that field and then delete all the duplicates at once. If there are no differences between the paired dives I am not sure what you can do to get rid of the duplicates other than doing them one by one

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I ran into a similar issue once where for some reason my dive computer got recognized as a new dive computer and so MacDive redownloaded all of my dives again. Luckily it showed up as a different computer name and I was able to filter the list based on that name, select all the dives, and delete them all at once.
I hope you find an easier solution than doing this manually.
Have a great day and have fund diving!
Shadallark