Make sure to delete the High Sierra installer app from the Applications folder ("Install macOS High Sierrra" I think) and empty the Trash before trying to download it again. If you still have problems, then repeat this and boot into Safe Mode to try again just in case you have some third party software installed which is interfering with the normal operation of macOS.
Also, why are you wanting/needing to reinstall macOS? If it is to resolve a problem, then you should include those details as the problem downloading the installer may be related to the original issue.
You should also be able to boot into Recovery Mode (Command + R) to access local recovery mode if you want to reinstall macOS (assuming you are currently running High Sierra). If your Mac only supports up to High Sierra, then a better option would be to boot into Internet Recovery Mode (Command + Option + R) to access the online High Sierra installer.
Do you have access to another Qualifying Mac which is compatible with macOS 10.13? This would include most Macs from 2010 to 2018. To confirm compatibility of another Mac you can use this article to see which Apple hardware is compatible with macOS 10.13:
https://eshop.macsales.com/guides/Mac_OS_X_Compatibility