Inactive Tutor answered 06/08/19
Honestly, I'm not sure about which plugin to use, but your best bet may be to export the google sheet to an excel sheet and use the Remove Duplicates feature then re-import it into Google Sheets.
I just double checked my Google Sheets and under the "Data" menu option, there is now a "Remove Duplicates" option. It says "new" next to it so it looks like they just added it.
Let me know if I can help!