“Corrupt data found, please verify your installation.”
This error message means that something has gone wrong with the engine installation, and you’ll need to either Verify your installation, which can be done by navigating to the Epic Games Launcher’s Library tab, clicking the arrow next to the engine version you’re using (4.12 in your case), and selecting the Verify option from the dropdown that appears. Or you can uninstall and reinstall the engine version as an alternative.
Let me know if you have further questions regarding this.