1st row - K1, cast off 5 sts (thumbhole), knit to end.
2nd row - Purl to last st, turn, cast on 5 sts, turn, P1
After you bind off 5 sts and knit to the end, turn your work and purl to the last st. before the bind off. Turn the right needle and cast on 5 sts, turn it back to normal position and purl the last st, which was the K1 from row 1.
Happiness is catching that dropped stitch while it's still fixable..