Picking up stitches from holder

Hi,
I am a beginner, and glad I found this site. I am knitting a cardigan and have the stitches for the sleeves on a piece of yarn. I finished the body, bound off and cut the yarn ball off. Now I have to go pick up the stitches of the sleeves and put them back on the needle. How do I reattach the yarn ball to these stitches? I’ve already moved them onto the needle and off the stitch holder, but don’t know how to start knitting again since the yarn ball is unattached. Thanks!
Mary

You don’t have to reattach the yarn there, necessarily. If you’re putting all your stitches back on the needle, you start knitting with a new strand if there’s not one attached at the place you need to start knitting.

You can just start knitting with it and weave in the end later.

I have good success taking the strand of yarn and leaving a short tail just looping it around the needle as if it was already attached and using the tail and main length of yarn and knitting with both for 5 or 6 stitches, then drop the tail and continue on knitting. When done go back and work remainder of tail into work with a needle.
Hope that helps.