Copy your new certificates to the SSL certificate location for Gitlab
cp sub.domain.com.crt /etc/gitlab/ssl/sub.domain.com.crt
cp sub.domain.com.key /etc/gitlab/ssl/sub.domain.com.key
Validate that this is the location that Gitlab will check for Certificates
cat /etc/gitlab/gitlab.rb | grep "ssl_certificates"
Should output:
nginx['ssl_certificate'] = "/etc/gitlab/ssl/sub.domain.com.crt"
nginx['ssl_certificate_key'] = "/etc/gitlab/ssl/sub.domain.com.key"
gitlab-ctl reconfigure
gitlab-ctl hup nginx