welcome, @wwcanoer to the community!
Excel does have a remove duplicates tool, on the “Data” ribbon:
Bitwarden import neither overwrites nor “merges” entries. In the premium plan ($10/yr), there is a reused passwords report on the web vault, which can help you find duplicate entries, but it too does not automatically remove entries from your vault.
There is a long-standing request for a duplicate removal tool/report that you might consider voting for.