Yes, I know this is probably very simple but I cant find it. I read the documentation, watch tutorials and cant find it mentioned. In UE3 you would right click the point to select it. I just need to create a Trigger volume and use the scaling tool to increase its size to the right, but leaving the selected point anchored where it is. 
in the ‘modes’ pane, select ‘edit geometry’ and then click the corner. you can also select whole faces or edges this way too.