Understanding pattern instruction

Could someone please help I’m stuck again on this pattern for a dress- the everyday princess dress. The dress is knitted top down with raglan and diamond pattern on front and back. I’m working the chart and now the instructions read:
Work at for 8 cm and you have nished a ws row, set the rst 6 sts (button band) on a spare needle, held in back of the work and knit it together in rib (p2tog k2tog) with the last 6 sts (button band). (3 stitches decreased)
Pm and join to work in the round and incorporate the charted pattern. It is possible to get a seamless result.

At the moment I’m knitting in flat, with circular needles. I don’t really understand how I can knit the button band stitches ( 6 in front 6 in back) together? And then to continue in the round ? Could someone please explain???

You’re going to overlap the buttonhole and buttonbands, knitting them together which will join in the round. It’s a little bit like doing the start of a 3 needle bind off. This project shows you the result of the overlap.