Each Atlas plan includes different features. Exporting imagery from Atlas is limited on the Atlas Lite plan. However, Lite users can still export the multiband GeoTiFF and DSM from your DataHub.
The GeoTIFF and DSM can be downloaded from your DataHub (see image), found here: Atlas DataHub
If you would like to export your current view and/or specific calculated indices from Atlas, please check out Atlas Standard and Premium. You can learn about this and all of the other available features in Atlas plans here.
If you are subscribed to Atlas Standard or Premium, and you are still having issues exporting your Atlas Imagery, please contact Support.