You can use tabular data to import data and add rows to an existing - empty or not - Cloud Collection.
Tabular sources are generally spreadsheets but can include other sources such as tables found inside spreadsheets, for example.
Media assets in the cells of your spreadsheet can be bulk uploaded using HTTP links or from an FTP server.
Here are some examples in a spreadsheet of different ways to setup bulk upload media assets: Spreadsheet demo for Batch Upload to Cloud Collection.
Once you have your spreadsheet built out you'll first need to create a new collection to add data into.
Here is an article on Basic Setup of a Cloud Collection Data Source
Once you've setup your Cloud Collection you can now Import Rows.
Simply select the "Import" icon.
When you import rows into an existing Cloud Collection, the column heading names must match those of the existing columns in the Collection.
Here are the columns from the spreadsheet you use to import your rows into an existing Cloud Collection:
Here are the matching columns in the Cloud Collection data source:
You can also add a prefix= modifier. Here is an example spreadsheet that uses an FTP server for the prefix for the column.
Likewise here is a spreadsheet example that uses an HTTP URL as a prefix.