How can a fallen arch be fixed?

Surgery: Is only way to change structure, but this is rarely necessary. Most often proper supportive footwear and orthotics will control symptoms. A flat foot is not necessarily a "bad" foot. Sometimes, no treatment is needed. Consult podiatrist.

Couple of things: Orthotics can be fabricated to support the arch or surgery can be performed to reconstruct the arch.

Orthotics: Shoes, surgery, braces treatment depends on severity.