Edge to edge stitch

How do you do an edge to edge stitch? I can’t find it anywhere. It is for attaching a collar to the sweater.

My pattern also calls for a slip stitch to put the seams together. I found a crochet slip stitch. Do you think this is the same?

Thank you to anyone who knows this.

I don’t know of a knitted slip stitch to seam pieces but you can do the crochet slip stitch for seams.
What do the instructions say exactly about attaching the collar?

The instructions might actually describe the ‘edge to edge’ stitch or how to do it. Do you have a link to the pattern.