Fix Wordpress Installation

We have a Wordpress site that has stopped working and need someone with Wordpress skills to fix it and make sure it is secure.
the URL is: http://www.fr.aerosurehcp.com/
The error we are currently getting is:
Warning: count(): Parameter must be an array or an object that implements Countable in /homepages/5/d463648754/htdocs/wp-asm-hcp-fr/wp-includes/theme.php on line 630
Warning: count(): Parameter must be an array or an object that implements Countable in /homepages/5/d463648754/htdocs/wp-asm-hcp-fr/wp-includes/theme.php on line 630

Warning: Cannot modify header information - headers already sent by (output started at /homepages/5/d463648754/htdocs/wp-asm-hcp-fr/wp-includes/theme.php:630) in /homepages/5/d463648754/htdocs/wp-asm-hcp-fr/wp-includes/pluggable.php on line 1195

After fixing there will be other projects on offer to improve but this project just covers fixing the website