This method is used any time an increase will be performed on the wrong side, which will appear as a left-leaning increase on the RS. The increased stitch is created after working a purl stitch.
Identify the purl bump 2 rows below the one on your right needle.
With your left needle, pick up this bar from bottom to top. This loop on your left needle is your new stitch.
Purl through the front loop.