How do i "tack" something

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.

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.

thank you, Ingrid–much appreciated. i’ll see if i am capable. so i’m bascially fixing the dropped stitch and then tying a knot.
hopefully i’ll be able to make it uniform.
amy’s video has come in very handy–unfortunately, i’m too far gone to fix it correctly.
THANK YOU