Compare records in 2 tables and move data from one table to the other

I have two tables with 3 columns in common: FirstName, LastName, Department. Table A (Access table) has additional columns (RecordID, Address, Phone, etc. This table is missing data in the some of the records in the Department field.

Table B (an Excel spreadsheet) is missing no data in any of the records. How do I compare the records in each table and move the Department data in Table B to the Department column in Table A where it is missing?