you don't. an Append query adds new records to a table, and that's it. to
"override" data in an existing record, you need an Update query to edit the
record. to replace the existing record entirely, you need a Delete query to
delete the existing record, then the Append query to add a new one. if you
want to replace specific existing records with specific new records, you'll
need to first identify the "matching" records that you want to "swap"; you
might try a simple Select query that includes both data sources, with a link
between whatever fields you're comparing to find matching records. then use
a Delete query to delete the records you don't want, and an Append query to
add the matching new records.
hth
