Help how do I soften these?

I've recently got these, ignoring the butterfly pattern I dislike they're really cute but expensive at nearly 100 pounds. (I couldn't find them elsewhere that was flat)

I tried walking in them today, really comfy but I've now got blisters at the back of my heel/foot

I wear medical innersoles but I think it's the leather,what can I do? 😭

Edit: The only picture they have are kids,the adults sizing definitely comes up narrower. (I hate that,I have proper shaped feet!)