I have a microscope that doesent work it was fine when I got it but something happened and it lookes like there’s dust or water or bacteria or something inside the lens what do I do?

That is not a lot for the basis of troubleshooting. First thing to figure out is the where in the lightpath you got issues and what kind of issues they are (misalignment, dirt etc.). You can always try cleaning the easily accessible parts (usually objectives and eyepiece) using safe methods and go from there.