I think there's a couple of ways. Do you mean that you have two tables with identical fields and do you want to add records from the second table into the first table?
You can do this with an append query. Create a new query add the first table to the query change it to an append query and select the second table as the table you would like to append to.
Run the query. If you have a lot of records it may take a while.
HTH
Rich