[Stiglr]

Try selecting both Objects and doing either Create Convex Object or Merge. Either way, that will make them one object (there may be a difference in how smooth the transition between the sections will be, since they do NOT match up where they meet right now). Then, smooth the ONE object until you get the visual results you want. Then, if you wish, you can select all the Surfaces that make up what was the purple part of the object and do a Cutaway Object to make it a separate object again.

If the Convex Object or Merge don't get you the right results, consider just extruding a few sections off of the yellow piece and recreating/reshaping the purple piece as an extension of the yellow piece, and then Cutaway Object to separate them into two again.