Sew a piece of the strapping below the end of the zip on both sides as you would fasten a normal strap. Leave one long edge going upwards need about , mine was 6inches ,yours will depend on your bag. Make it longer than you need as you can cut down put hard to add on. This is where I would put my Dring and you can decided where you want it. Make sure the ring is big enough for the strap. I make my strap width of the straight section. Look at a long handle on a purchased bag and copy . You could do it double and put one of those squeeze and slide things or make so you can adjust length .
Those extra sections make it easier to keep out of the way of zip.