How do i "tack" something

[lulabee]

beginner knitter here.
problem: i'm knitting a shrug. and what i thought was just a loose stitch has turned out to be a dropped stitch a LONG way back--and it's rather a mess. the lady at my knitting store told me i'll have to tack it--and i'll have to take a class in order to learn how to tack it.
i'd rather not take a class and undoing the work is not an option for me.
any help?
THANK YOU.

[Ingrid]

If you just want to secure the dropped stitch, I'll tell you what I've done and it works great. Pull the loop through to the wrong side. Then take a tapestry needle with the same yarn, or a crochet hook, and pull yarn through the loop of the stitch above the dropped stitch, through the dropped one and through the stitch below it. Tie a little knot and weave in the ends.

If you want to correct it, you could try to use a crochet hook to bring it back up as in Amy's video.