How to recycle an old sweater (or a botched one) into usable yarn

Step 7 Find the end stitch and undo the finishing knot.

Now, find the very last, cast off stitch. This will typically be on the front side of the knitting(the knit side) at the left end. (Note: If you see the v's going in the opposite direction as those in pic 5, flip it over and look for the end knot there.)

Pics 1 & 2 show the locating of the finishing knot on the knit side of the swatch and the undoing of it.

Pics 3, 4, & 5 show the yarn being liberated from it's knot. Now you can rip out the knitting as shown in steps 2 & 3.