It’s very tough to tell exactly what the issue is from only this PHP warning, but it seems to be related to the car_repair_mechanic_setup() function within your theme. Since you can’t reach the admin of your website, I’d suggest changing the name of the folder on your server at /wp-content/themes/car-repair-mechanic/. That should allow you to access the admin of your site again by disabling your current theme.
If you need to use that theme, another potential step would be to turn on debug logging. That will store errors and warnings in a file, instead of showing them directly in the browser. You can read all about this at https://wordpress.org/support/article/debugging-in-wordpress/, but you’ll generally want the code in wp-config.php that outlines your site’s approach to debugging to look like this:
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_DISPLAY', false );
define( 'WP_DEBUG_LOG', true );
Please keep in mind that this debugging configuration shouldn’t be used on a production server since it may be viewable by anyone on the web.
Neither of these steps will solve your root problem, but hopefully they make it easier for you to access the admin of your site and debug the issue.