Mending a leather jacket beginner

I got this leather jacket for free. It’s genuine leather according to the tag, it’s very thin leather so I’m having a hard time finding information on how to mend it.

I don’t have a sewing machine. I have regular thread and embroidery floss, I was thinking I should glue flannel to the hole and then sew the edges to secure it, but I’m afraid it will tear the leather more.

I’m hoping someone can leave me tips or suggestions on how to properly fix this without making it worse.