Blob Storage Rest API doesn't support a bulk operation for blob deletion. So, the alternate way is to use AZ CLI and go for a bulk deletion. The steps are pretty much simple
As you never tried az cli, start with the az install as explained in this reference: install-azure-cli-windows
Once the installation is succeeded, login az cli
az login
Run the following ps command to delete all the contents within the container. I am using a pattern * to delete everything
az storage blob delete-batch --source "your blob container name" --account-name "your storage account name" --pattern *