Reverse seam for garter stitch

I was looking at a pattern for a hat and it ends with:
reversing seam for a 3 in. (7.5 cm) at cast-on edge for ‘cuff.’

This is a garter stitch hat.

So, what exactly does this mean?
How do you do it?


Usually you use mattress stitch to seam something, working from the RS so the edges are on the WS. But the lower edge will be turned up so you would seam with the WS facing on that part so when the cuff is rolled up you won’t see it.