In Labeler, with the barcode on the screen, right click on the code and select source.

On this screen click the "Convert to Substrings" button, then click "Yes" on the confirmation box.  The barcode has now been split into two parts: 1.000 and 1.001

Select Barcode 1.000 then go to the Static Options tab.  In the field provided type in the first part of your data (ABC in the example).  Click the Apply button, then go to the Substring Details tab.   Select whether this data is to be shown in the Barcode or the Caption, or both.  Once your choice has been made (in the example we don't want ABC to show in the caption, so we'll uncheck the Include Substring in Bar Code Caption option) click the apply button and select Barcode 1.001 

Once Barcode 1.001 is selected, go to the Static Options tab.  In the field provided type in the second part of your data (1234 in the example).  Click the Apply Button then go to the Substring Details tab.  As before, select whether you want the data entered here (1234 in the example) to show in the Caption, the Barcode, or both (in the example we want the 1234 to both scan and be readable in the caption so we leave both options checked).  Click Apply when you are finished here, then click Finish.