Setting password for MySQL root user in CLoudSQL with private IP address

How to change the password for MySQL root user in GCP CloudSQL DB instance with private IP address . I am able to change the password using the below command from Cloud Shell with Public IP

    gcloud sql users set-password root  --instance=testdb --prompt-for-password

but it does not work for instances with Private IP address .

I can use the GCP Console to change the password but the root user is not listed under Users TAB

Console--> CloudSQL--> DB Instance --> Users

Other option seems installing gcloud on a VM in the same network as CloudSQL and change it using below command

gcloud sql users set-password root  --instance=testdb --prompt-for-password

Any other suggestion to change password for root user in a MySQL private DB instance . I need to change the password as initially the DB was created skipping the password.

Also is it more secure to use --host=% option while changing the password with gcloud command.

gcloud sql users set-password root --host=% --instance=testdb  --prompt-for-password