Once you have set an association between two entities in a domain model, especially if it's an association between entities from different modules, it's very difficult to drag these lines to make them overlap less or realign them. Most of the time it starts to draw a new line.
It would be useful t make it easier to select an existing association line and drag it.
If you select the association first, you can drag the points way more easily than trying to do that without selecting the association first. This might help you.