Completing a yarn over (YO) on the purl side of your work is the same process as on the knit side. The only difference is that the working yarn starts and should end on the front of your work. This can get a little confusing for knitters, as it seems like the yarn is being wrapped around the needle too many times.
The trick is to focus on where the working yarn needs to be in order to work the next stitch. For a knit stitch, the working yarn should be in the back, but for a purl stitch, the working yarn needs to be in the front of the work. This is why after the yarn is draped over the right needle, the counter clockwise motion continues so the working yarn is brought back to the front of the work so the next stitch can be purled.
Whether it's completed on the front or back of the knitted fabric, the purpose of the YO is still the same. It creates an intentional hole that has many uses for our knitted fabrics. The tutorial below will guide you through the steps to complete a yarn over the the purl side.
Start in the front, end in the front
Starting with the working yarn in the front of the work, lay the yarn over the right needle. Continuing to move in a counter clockwise direction, bring the yarn back to the front of the work so you can continue purling.
Continuing to work on the purl side
With the working yarn in the front, you can continue to purl the next stitches or complete any decreases that often accompany a yarn over. The instructions from the pattern will guide you on what to do next.