My personal, n=1, experience with “fixing” feet:
Tree climbing and walking on tree roots.
Sand walking at beach hard and soft sand.
Jungle gym / monkey bars climbing and playing.
Walking or climbing on, through, over, around stone, rocks, curbs, walls, etc.
In work or home environment – pvc pipes of varying dimensions, lacrosse balls and batting cage softballs and golf balls and marbles (whole and half), 2x4s 4x4s 2x8s wood, slant boards (homemade)…. always standing squatting crawling shifting on these and other 3D surfaces as often as possible.
(Get into the right environment/setting, then let mindless creativity and unlimited play take over.)