In order to install velero-notificacionts, first add this repository to your Helm repos:
helm repo add zokeber-velero-notifications https://zokeber.github.io/velero-notifications/
After that, you can run helm search repo zokeber-velero-notifications to see the charts.
helm install velero-notifications zokeber-velero-notifications/velero-notifications
Please looking at the Helm Chart Readme file to setting up or overriding some values.