Web & desktop app
To promote a subitem, press
Shift+Tab. It “pulls out” the item by one level, which is useful for starting another list.
First, focus on the item you want to promote. This will bring up a sliding toolbar will appear at the bottom. You can then tap on the un-indent icon to promote it by one level.
Shift+Tab shortcut is not supported while using external keyboards with the iOS app, we're really sorry about that and are working on a fix.