That depends upon the outcome of the Permissions repairs and what the dism and sfc /scannow cmds report to see if they sort those Access Denied problems on those cmds or the update problem.
If that 1803 ISO is downloadable, you can use Windows USB/DVD Burner Tool to create install media of your choice and perform a repair install, which would be my preferred method of resolving most Win 10 problems.
https://www.microsoft.com/en-us/download/details.aspx?id=56485The repair install which doesn't affect personal stuff or installed programs is done from within Windows by opening Windows/File Explorer - This PC - insert the install media and double click on its drive.
This will start the process when using a DVD but will open to its files when using an USB where you would then double click on setup.exe Application.
If you were using 1903 then a repair install wouldn't be an option as that is a bug in 1903 where it snags the install media as hardware incompatible with that version of Win 10 which MS are aware of.
The only option then would be to perform a Reset which keeps your personal stuff but removes all of your installed programs.
I've had to do this recently on one of my Win 10 machines after updating to 1903 because I was getting a MMC error when trying to access Event Viewer.
