I am forever informing my customers about the importance of installing a good extractor fan in a showering environment. Some of them do, some of them don't. Going back to a job I did 6 months ago to fit one in a shower room, the moisture is running down the walls.
All you can do now is try to scrape out the grout as best you can and redo it. But be warned, the edges of your tiles will almost certainly sustain some damage.