You need to cut a piece of fabric of similar weight and a stretch behind the tear but instead of zig zag, try sewing back and forward into the grain of the fabric. If you really look at it you will see lines (usually) on an angle. This is the weave of the fabric. If you find a thread colour similar to the colour of the jeans, then you secure the piece of fabric behind and stitch back and forward to cover the tear. If the tear is close to the seam, unpick the seam. Do not try and repair over a seam. It doesn’t work. Take the extra time to have easy access to the tear. You will be happier with the finish repair. Also. I use a product called vizafex. It is a two sides sticky used in appliqué. I use that to secure the fabric behind. One side peels off and you iron that on to one side, then you peel off the other piece of paper and iron it to the garment. If you would like to see a photo of what I mean, email me
Judith aka genie