Altering dress, hand sewing

[ZigZagCarrot]

There's a dress I think DD would like on Vinted but the back has a cut out thing that she'll probably find irritating.

What is the easiest way to change it to regular vest type straps by hand? I was thinking use some of the cut off unnecessary bit to make the edges look neater? I've done quite a bit of sewing but not clothes making or correct hems (except simple stuff for dolls!) thank you in advance.

Don’t know if this is too late, but two suggestions

1. it looks like the panel for the horizontal ‘bar’ is sewn onto the outside of the simple straps of the tank top. You might be able to unpick the seams and then just remove it. You then just fold the edges back of the simple straps and then sew straight stitch down to re-hem. That would probably look best unless these’s something weird underneath

2. if that isn’t possible, you could trim away the excess fabric, leaving double the width of the seam allowance. Then fold it under twice and sew down the hemline.