Knitting 2 pieces together horizontally?!?

I have a piece that I’m working on which is almost complete. All I have left to do is knit two pieces together. I’ve looked at the various videos on how to do this, but every example showed the person knitting them together vertically. I need to knit my pieces together along the sides that were originally casted on. Is there a way to do this well???

Check out ’ 19: STITCH TO STITCH OR HORIZONTAL SEAMS’ chapter here