Sewing Neat Purls on a slipper seam

I finished my cuffed slipper. However, there were no instructions for how to sew up the slipper (I’m used to knitting in the round so I am clueless). There are purl stitches at the edges that need to be sewn. I checked my knitting book and the instructions in there are for the side seams of a sweater. I would appreciate any help. The slippers are Cuffed Slippers by Barbara Breiter (sp?).

it looks like garter st edges that need a seam or the cast on at the back of the heel You can use mattress stitch to seam the garter st
I usually just use an overcast sewing st to neatly seam the heel on slippers like these. Very cute pattern with the cuffs!