Hi and welcome to the forum
Dwarf Gouramis (Trichogaster lalius) carry an Iridovirus that causes sores appear on their body (like the blue fish in the picture). There is no cure for the Iridovirus but you can sometimes treat the secondary infections and try to build the fish's immune system up so the fish fights the virus and recovers.
Adding a vitamin supplement to the fish's diet and doing 75% water changes and gravel cleaning the substrate each day (or every couple of days) can help strengthen the fish. Make sure any new water is free of chlorine/ chloramine before it is added to the tank. Make sure the temperature is 26-28C (79-82F) so the fish is more comfortable and have some floating plants in the tank for shelter.
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Dwarf Gouramis also carry Tuberculosis (TB) and this is a slow growing bacteria that builds up in internal organs in the fish. Eventually the organ ruptures and the fish swells up, stops eating, does stringy white poop, hangs around the surface or near a filter outlet and breathes heavily, and dies within 24-48 hours of showing these symptoms.
There is no cure for TB.
If you suspect the fish have TB you should wash your hands and arms with warm soapy water after working in the tank. Do not put your hands in the tank if you have any open wounds (cuts or scratches). If you have any sores on your hands or arms that don't heal quickly, tell your doctor you keep fish and ask them to take a swab of the wound and test it for TB. Do not take any anti-biotics until you get the results back because different strains of TB require different drugs to kill them, and if you take a medication that does not kill the bacteria, it can make it harder to treat.
Most people never get localised skin infection from their fish tanks but people with a weak immune system (diabetics, heart disease, etc) are commonly infected. Avoid getting tank water on open wounds and washing with warm soapy water will normally prevent any infections ever occurring.
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Try not to buy Dwarf Gouramis or any of their colour varieties until the Asian breeders fix these issues, which could take a while.