Can anyone explain how to decrease this

Im struggling with decreasing the armholes with this dress

any help would be appreciated
Thanls.in advance

Which size are you making? 1st, 2nd,…?

Its the 3rd 12-18 months

Every 2 rows means every other row. You are binding off at each end of the row. The other thing to remember is that since you can only really bind off at the beginning of a row, you’ll have to bind off, work to the end of the row and turn. Then bind off at the beginning of the next row.

Start with 67sts. At 41cm, bind off 2sts at the beginning of the next 2 rows. Then bind off 2sts at the beginning of the next 6 rows. (That’s the equivalent of binding off 2sts at the beginning and end of 3 rows.) Then bind off 1 stitch at the beginning of the next 4 rows (47sts)
At 51.5cm bind off the central 21 sts. (13sts per shoulder). On the 2nd row at the neck edge, bind off 5sts (8sts remaining)…

Thank you so much I was really struggling