You're not increasing, but casting on more stitches for the underarm. It will be when you come to the point where you bound off the 32 stitches for the opening. Then knit across the next 58 stitches for the front and CO 6 more. The extra stitches will be on the next round you knit.
If you're not sure how to cast on in the middle of a piece, go to the cast on section
and look up knitted, cable or backwards loop castons.