Does it leak? Find out the metal type, use a magnet if necessary. It is probably a roof coating of some type. You may get away with putting a fibered roof coating back on it again. But I would be sure to remove any loose material and clean the remaining surface including sanding or at least scuffing the rust.

@millworkman I have not seen any sign of a leak but absence of evidence isn’t evidence of absence. The metal does hold a magnet, so it must be steel.

Would this be a DIY task? It seems like a small enough job that a roofer might not be interested.

Roofer would definitely not be interested. You could DIY or a local handyman may do the work for you. Roof coating can get a little sloppy.