How to upgrade to the new Grafana Alerting on Cloud Free Grafana.net?

Hi All
I have received the following alert on my “Grafana legacy alerting is going away soon” on my X.grafana.net/alerting/list console.
After reading the documentation, I am still unable to figure out how to enable the new Grafana Alerting. Where do I find custom config for Cloud Free Grafana instance?
“In your custom configuration file ($WORKING_DIR/conf/custom.ini)”

how to enable the new Grafana Alerting feature.