1/ Soaking in water will soften them temporarily, if you want to get them to fit better.
2/ Dubbin, from a shoe repair shop, will soften permanantly, but it takes off any shiny finish.
The shoe menders used to sell a leather softening spray that you sprayed on the shoe then put the shoe on & it moulded to your foot. Can't remember what it was called but if they are still selling it the shoe mender will know what you mean.
I think you mean 'leather stretcher'. Doesn't actually stretch the leather, it temporarily softens it, then you put the shoe on and it moulds to your foot. You can still get it at most shoe repair shops. Doesn't soften the leather permanantly though.