I wouldn't risk using an iron on leather.
Yesterday, I tried the hot cloth, tennis ball combo (hockey ball in this case - live next to a hockey club and gets loads in garden, knew they'd come in useful one day)

Additionally I gave it a blast with the steamer. Indents are about 70% reduced, so think with another go, it should do the trick.
Only slight annoyance is that the studs or whatever have actually marked the leather so even when the indentations are gone there will still be some marring! Just have to live with it.
