Select the left vertical face to create the curved junction:
Select 4 junctions on Mechanical Browser and click the Disable () button on the context right-click menu
Hover over the right vertical junction face, click the Smooth faces () tool button, on the Select section of the Quad.
Hover over the vertical junction face, click the Push/Pull () tool button, on the Model section of the Quad and move the cursor to the endpoint (5 mm) of the left vertical face.
2. Rework the right side of the border
Click the Dissolve () tool button on the Modify panel, of the Sheetmetal tab, on the Ribbon. Hit Enter.
Click the Slice () tool button on the Edit panel, of the Solid tab, on the Ribbon. Select the body, hit Enter. Specify 3 endpoints in the corner to specify a slicing plane and hit Enter to retain both parts.