The pattern of the sleeve of right and left is the same.Distribute the 12 stitches from your scrap yarn onto three double pointed needles. And join new yarn, Pick up 4 stitches at underarm.
Then k2tog(with the stitch<make one>which you picked with the left needle)
k10,slip 1 stitch knitwiseThe next work begins to pick up yarn under the first stitch of the next needle,and makes 1 stitch.The stitch is twisted,and it's to the right needle.Then you cover the stitch with the right stitch(slip 1 stitch knitwise),k2,pm(A marker is in the middle of the underarm)
Bind off in purl stitch. 4.5mm of needle.