You can do one of four things:
1. You can lube the chain and hope it works.
2. You can try a special chain cleaning device (These can be found in bike shops, though I've never tried one).
3. You can replace the chain (Probably the best option, but you will need a chain removal tool).
4. You can put it in a bucket then mix some water with some Muratic acid and let it set for a week. (My uncle used to dip rusted (Muratic acid eats rust) car bodies and leave them for a week and they would come out looking like new.)
1. You can lube the chain and hope it works.
2. You can try a special chain cleaning device (These can be found in bike shops, though I've never tried one).
3. You can replace the chain (Probably the best option, but you will need a chain removal tool).
4. You can put it in a bucket then mix some water with some Muratic acid and let it set for a week. (My uncle used to dip rusted (Muratic acid eats rust) car bodies and leave them for a week and they would come out looking like new.)