I cut the elastic waistband off.
Opened the two side seams with a seamripper long enough to go from my neck to under my arm plus an inch or so to make the new casing for the ribbon tie.
I then top stitched the new arm openings.
Then I folded down the top edge of the fabric about an inch and topstitched the new neck casing.
All that was left to do was thread a black ribbon through both the front and back casings and I had myself a new one-piece wearable upcycled dress!