Bitwarden imports everything in the file you give it without deleting anything from your vault.
I see two options :
If you did not change anything in BW, then wipe your vault and import again
If you made some changes in BW that you want to keep, make a CSV export of your BW vault and use a program like Excel to find the entries in your last pass export that are not in BW
I figured out how to wipe/delete the vault. Two ways I believe. You can “purge” the vault and I would guess that wipes it in one shot, or you can do it like I did by selecting all the check boxes and then deleting them. That way would probably take a little longer but you can be selective if you need to.
I then re-imported my lastpass information and it worked like a charm.
One thing I noticed though, there were some duplicate folders with nothing in them although the original of those duplicate folders did have the correct info.
So now I need to figure out how to delete those duplicate folders…