In Creative Suite locate the creative you wish to download

Click on the Download or Publish icon or click on the Kebab menu (3 dots) along to the right of said version and then select Download.

Select the network(s) for which you want to export a build for.

Click Download.

Navigate to the your concept's creative page in Creative Suite.

Select the creatives you want to download.

Select click on the Download or Publish button located at the top of the creatives table.

This will take you to the download page and you can check the number of creatives you're about to download on the left side:

Select the network(s) for which you want to export a build for.

Click Download.