Problem with WordPress (WP) theme preventing WP log in


I am learning to edit the Themes Function.php file in SemPress theme. I made a change to the code for the register_nav_menus function and then tried to restore the original code by copying it back in.
I got this message:
Parse error: syntax error, unexpected ‘;’ in /home/suzdav/ on line 84

Furthermore, WordPress is no longer allowing me to log in and access my dashboard. What should I do to fix this?

Posted this on the WP support forum 4 days ago but no response yet. Please assist.

Upload a clean copy of the theme’s functions file via FTP.

And then create a child theme and use that to make changes. NEVER edit theme files because…well, I think you know why.

Thank you very much kjodle.

I successfully uploaded a clean copy of the file and found a free, helpful plugin called ‘One-Click CHild Theme’ for creating my child theme.