You’re here to get your site up and running again, and to that end, we’ve collected several different potential ways to fix the issue. Knowing that the cause is likely PHP-related, these may involve editing core WordPress files. Even with your site in a broken state, make sure to back it up before implementing any of these suggestions, as we don’t want to make it worse!
If you’re able to log in to your website’s backend, that will help immensely. But as your entire site is likely down, you’ll very likely need to access it through FTP (or SFTP).
Contact your web host or look through your hosting dashboard to find your FTP login credentials, and make sure to install an FTP client like FileZilla. This guide on connecting to WordPress over FTP can help too.