How to Merge Excel File to Mailing Labels (With Easy Steps) So, in that case, we need to create a custom layout to merge excel files to mailing labels. Follow the simple steps to do this. To begin with, go to the Mailings tab. In addition, select the option ' Insert Merge Field ' from the ribbon. A new pop-up window named ' Insert Merge Field ' will appear. Then, select a new field and click on insert.