To move or copy items between folders in Blackbird:

You can open a files window by left clicking the folder icon on the left hand menu

Then open a second files window by right clicking the folder icon on the left bar of Blackbird and selecting "New Files Window" or if you already have multiple folders open you can quickly toggle between them and enable or hide them

You can then left click drag and drop to move items between folders or right click and drag and drop to copy them (only the item will be copied, not source media if high bitrate content is referenced by the item.