Any way to undo the action in OpenStudio?

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There is no undo. Did you save a backup? You should always backup OpenStudio files. Otherwise, you can try to restore the file to a previous state, or, if you tried to simulate it, you may have a residual file saved in your temp directory. From your prior questions, I think you are using windows, so this would be in your Users\<yourname>\AppData\Local\Temp directory.