Hi. As the others say, yes it would be a good idea to take your hamster to a vet. Wounds can turn septic. Also if your hamster is sharing a cage the wound could be being re-opened when they fight. You might not see them fight, but if they have started this can often lead to one killing the other and/or some serious injuries to both.
I think you should separate them now, as Shannon says. And take the one with the injury to the vets. So you will either need to get another cage quickly, or make a bin cage out of a plastic storage box as Shannon suggested, but this will need holes cutting out and mesh ventilation putting in.
Although you can get a bin cheap, by the time you have got all the bits and pieces it could be easier to buy a not-so-expensive cage.
This would be good for a Robo (Ferplast Multy Duna tank)
Cage Duna Multy
Dwarf hamsters can live happily together for a long time but once they start fighting and causing an injury it is an urgent and serious situation and could be expensive in vet bills as well as the hamsters suffering.
Apologies if I've misunderstood and your hamster isn't sharing a cage at the moment. But if they are sharing a cage then they need to be separated now. So it might be quicker to buy a cage or duna tank locally.