Breaking in your new shoes.

https://www.shoezone.com/Blog/how-to-break-in-new-shoes

Taking the time to break in new shoes can be the difference between falling in love with your new footwear and hours of painful, aching heels. New shoes are great – especially when they fit our style. They look amazing, feel comfortable and support our feet. Until they start to rub a little that is. Shoes fresh off the shelf usually need a bit of breaking in – or wearing around the house – so that the material loosens up and ensures a comfortable fit for your feet.

They don’t take long to wear in and breaking in new shoes can help prevent potential blisters and extend the life of your new kicks.

https://www.collinsdictionary.com/us/dictionary/english-thesaurus/break-something-in#:~:text=to%20use%20or%20wear%20(new,prepare

break something in
(phrasal verb)  in the sense of prepare
Definition
to use or wear (new shoes or new equipment) until comfortable or running smoothly
I'm breaking in these new boots.