Have you ever mended lined pants? Ordinarily I would use my sewing machine to stitch over the tear, but that would make the inner lining pull funny when it’s worn.
To begin, I trimmed off the unraveled threads that were hanging off of the torn area.
Then I got out some scraps of fusible interfacing I had lying around and I cut strips just a bit wider and longer than the length of the tears.
Next I placed the interfacing with the fusible side up, sandwiched between the lining and the jeans, and ironed it down from the back side (because the pocket was in the way) until the interfacing stuck.
Lastly I stitched the torn edges together using blue thread, being careful not to catch the lining on the needle.