If you need to merge a large number of addresses together this is best done by exporting all Addresses from CartonCloud, Merging them within the exported CSV using the method outlined below, and then uploading the saved CSV to CartonCloud.
Step-by-Step Guide
Step 1: Export all Addresses by select More in the main menu, followed by Addresses in the drop-down menu.
Then select the More button on the page, followed by Export to CSV in the drop-down.

Step 2: Open the file in Excel or your chosen spreadsheet processing program and add a new column next to 'id' called 'merge_id':

Add a filter to the top row (highlight Row A and then click Filter)

And order your addresses by Name:

Scan the list looking for repeated addresses. An example here is Adelaide Fresh Fruiters, there are 4 addresses which are actually the same address.
By copying the ID of the one you want to keep into the merge_id field for the other addresses. This will cause the addresses to merge INTO the original address (so only the address with id: 9623 will remain afterward).

To save only a small file (rather than processing the entire file when you upload), once you have finished adding merge_ids, go to the top of the list and click the dropdown on the merge_ids column, then uncheck (Blanks) and click OK:

Copy and Paste the contents of the sheet to another worksheet:
Select everything visible:

Create a second worksheet:

Paste into cell A1:

Then Save the file (Ctrl+S) - this will override the CSV file you downloaded.
Now import back the file back into CartonCloud by selecting the More button, followed by Import CSV in the drop-down.

Select the file you just saved, and click Upload File.

The addresses you selected will now be merged in the system.