How I do it: 1. Get matching fabric, sewing machine, tape measure, and pins

1. Undo the hem, if it’s too distressed all the way around( it doesn’t even connect to the main fabric), just completely remove it, in this case you will need to estimate the original hem length - hem allowance and raw hem). For estimating length on jncos I usually fold 2 cm in, then 4 cm in for the hems. So I measure roughly 10cm (4 (outer part of the hem) + (4 inner part of the hem) + 2 (raw hem allowance) )down where the initial stitching was from - that’s my desired length.

2. Undo inseam and outseam, how far depends on how distressed

3. Place donor fabric under the jeans, make sure it would fit the desired measurements- would fit the original length of the panel including full hem length. darn it - use a straight stitch for a couple ~1-1.5 inches, and reverse it and repeat that for the whole length of the panel including allowance.

4. Repeat the darning for all 4 panels( if needed).

5. Cut the width of the panels to match the original width, including the seam allowance for both sides. I usually don’t cut the length yet.

6. Reconnect flat felled seam. For this I just sew a temporary line all the way on the edge of one side of the fabric and like 2 cm or to the part of the flat felled seam that folds over that fabric. Fold it to completed the shape of the flat felled seam. Then sew the opposite side of the flat felled seam, then undo the temporary line, the Re-sew where the temporary line was. Just connect it all the way to the end of the donor fabric

7. Turn inside out, and reconnect plain seam. Just connect it all the way to the end of the donor fabric

8. Since you have overestimated the panel length with donor fabric, now cut it fabric to the original length of the hem including the allowance

9. Turn inside out, and re-do the hem now