If you can’t solve the problem by flipping the slur with F, then unfortunately you’re out of luck at the moment. However, I’m always thinking about where the functional divisions are between each of the products in the Dorico family, and in future versions of Dorico Elements we expect to introduce the “graphical editing” tool in Engrave mode, which will then allow you to drag things around as needed. There’s no timescale for a new Elements update at the moment, however.