You have created two address books (e.g. addressOne, addressTwo) and each of them has the same format and contains different records. You want to merge those two address books into one.
After you click the Open button in the Import file window, you will see that the two address books have merged into one. To save the address book, you need to click on the File menu in the address book window and then click on either Save or Save as. The Save file window opens. Enter the file name you prefer (e.g. addressbook) and choose the path where you want to save the address book file. Keep the saved file type as Tab delimited (ASC).