I used to suffer from plantar fascitis. I had to wear customized orthotics to support my feet every day, in every shoe I wore. No walking barefooted, or sandals.
Then, when reading a book written by a chiropractic colleague, I discovered the “short foot” exercises. They are a designed to improve the function of the muscles deep inside of the feet.
After a few weeks of doing these exercises, my pain left, and hasn’t come back.
I remembered these exercises after reading this article about runners who did the short foot exercises and got better.
I have a few videos on how to do the short foot exercises on this website on the Exercise Instructions page under the Foot heading.