how can I fix a corrupted indesign file

You don't give enough detail to provide a meaningful answer, and it is possible you will need InDesign tech assistance in any case, but some things you can consider;

1. What version was it created in, what version are you opening in? If they don't match, try using the same version and, if that works, try saving to IDML to move.

2. Does it crash on opening or crash when you try to do anything? For example, I've had a file wipe out the server due to pasteboard dimension sizes. I could open the file, but just not do anything without crashing. So I scripted a change to reset the pasteboard and the files opened.

3. If all else fails... Do you have an earlier version you can revert to and then reapply the changes?