Copydex is not strong enough to repair leather, there used to be a product
called vinyl weld from loctite, first get a scrap piece of leather bigger
than the tear, insert it under the tear in the leather, then squeeze in some
impact adhesive out of a tube under the tear & between the original leather
& the repair piece you have stuck in, wipe excess glue off with a rag soaked
in white spirit, after 15 to 20 mins gently press to make join strong, leave
over night & then fill the scar with the vinyl weld, when it dries it sinks
a bit so 2 or 3 applications may be needed, any excess can be trimmed off
with a sharp craft knife with a curved blade, this product it clear in
colour so you will need to mix an appropriate colour with craft / modellers
paint, when dry buff it over with some boot polish, job done,

Steve68s,