For restart VPS we already give Administrator or root Password of VPS. By login you can restart your VPS.
Such as centos VPS the command is " reboot now "
If you failed to login and need reset password or restart you open a support ticket with details such as IP and others related inforation.
We reply as soon as possible.
User: your login email
Password: Provided to you email
Then go to service details & available action show in Interface.