You are looking for the Tangent Arc command.....
Tools > Sketch Entities > Tangent Arc
Delete the line at the bottom of your relief then add a Tangent Arc in its place.
You do not have to predeleted sketch lines as you can use the 'sissors' function to delete any sketch segments that you don't want to retain between contact points. A very useful approach. Note that if you delete a dimension reference point you may have to re add the dimension.
Thanks Anna & Kent