You can drag items in the queue up or down the list to change their priority in real time. That way you can set the next item to be processed by dragging it all the way up to the top. Note that the priority is changed in real time, it doesn’t save it, so it if you stop the engine and restart it you’ll lose any real time changes you made to the queue priorities.
This feature has been around for a while: Drag/Drop or Right Click ability to Move and Reorder Pending Conversion in GUI