MS Excel: Compare two columns and delete duplicates from just ONE column

I have column A that is 1,500 records.
I have column B with 40,000 records.

Among the 40,000 records in column B, duplicates of ALL 1,500 records from column A exist.
How do I find WHERE the 1,500 dupes are and how can I delete JUST those records?

In Column-C use something like this (adjusted for your actual ranges):

=MATCH(B1,$A$1:$A$3,0)>0

Note the use absolute references for the column-A.

Which will return either TRUE or #N/A. Extend the formula down column-C for as many rows as usedin column-B.

Next, use Advanced Filter with criteria and the option to copy the non-matching entries to another location.

Make sure column-C has a header say, “Match” (w/o quotes)

For the AF criteria cell use: ="<>TRUE"