If it's composite armor like a lamellar, coat of plates, or brigandine then it can be disassembled for the plates and reassembled. Making iron plates was rather expensive for most of the Middle Ages.

And if it's chainmail, you just shake it until all the crud and rust is rubbed off and patch the holes.

Plate would be significantly harder to get back to original condition from damage, and cloth armor and padding such as gambesons would be a lost cause