How to Fix a Pulled Thread
Never cut a snagged thread in a sweater; you'll end up with a hole -- and more work than simply repairing a pulled thread. Instead, use a large blunt needle to gently work it back into its proper place in the fabric.
Turn garment inside out. If pulled thread has caused fabric to bunch, gently stretch it back into shape. (Some of the yarn will go back into place.) Use a large blunt needle to tease thread back into position: Pull thread through to the next stitch and then the next, dispersing excess along the row. Repeat on other side of snag. Once thread is in position, smooth pulled area, and steam.