I see the only way to do this is to touch trace-right button click- for each one. Is there a faster way to do this like when you stretch beveled corners, can you add arcs with just one button click? Can you grab an outside trace to have both of them arc at the same time?
Selecting the trace segment, doing a right click and choosing Stretch Arc or Create/Modify Arc is the best way to add arcs to existing traces. Selecting a trace segment in a group of traces will only add the arc to the selected trace. Adjoining traces will move out of the way if Plowing is enabled but they will not have an arc added.