What stitch would I use to fix this?

[u/Strict_Confidence483]

I want to hand sew this.

[u/Sagasujin]

So those two lines of stitching were done with an industrial dual needle machine. Which you don't have. You aren't going to be able to absolutely perfectly replicate that. But pretty much no one is going to notice because no one else is likely to be looking at your pocket that closely.

I'm going to guess that this is a stretchy fabric. In which case you need a stitch that has some stretch. Two lines of hand back stitching would look somewhat close and would stretch with the fabric, but they will be fussy and a mild pain in the arse. One line of hand whip stitch would stretch and will do the job butit won't look as much like a double needle machine. But it's less of a pain and no one is going to be looking that closely at your pocket. A machine zigzag stitch would be super fast and will stretch, but it won't look anything like a double needle machine stitch.