Take hold of the 2 outer layers and put them together so that the right sides are together, lining up the raw edges.
Fold the tag in half widthwise and insert it between these two layers about 4cm away from the zip. Use pins or clips (depending on your fabric) to help hold it in place. Make sure the short raw edges of the tab are lined up with the raw edges of the outer layers.
Take hold of the linings and do the same, except you won’t need to insert the tab. Make sure the zip ends are pushed towards the lining. You can pin the side seams of the lining.
Stitch down the side seams making sure you use the hand wheel at the zip as the layers will be too thick at this point.