Repairing a leather chesterfield - any ideas/tips?

[Flightattendant4]

I've just got a second hand armchair, which is classic chesterfield type - buttoned leather all over.
It's a nice old one, but has a big bit of damage on one arm. I'm going to have to sort it out as it looks pretty bad, but haven't a clue where to start. I do have some old leather and was thinking of just patching over it, and then dpoing the same on the other arm to match, but it is a different colour to the rest of the chair and I wondered if there is a better way or some company who can repair this sort of thing, if I paid them.

TIA