There is a product called “Sheepskin freshener” or “Leather freshener”. I use it on my loafers and it works just great. The brand I have been using is UGGs actually.
Also there is a kind of ball like product, which you screw open and put in your shoes over night. It can be used more than once before you will have to buy new, but is just permanent.
Hope this helps.
Which one are you referring to?