prosite login problems https warning dashboard

Hi, I am creating test accounts for my site, and when i try and login as a user i get this warning Your connection is not private

Attackers might be trying to steal your information from (for example, passwords, messages, or credit cards). NET::ERR_CERT_COMMON_NAME_INVALID
Automatically report details of possible security incidents to Google. Privacy policy

Why is this? How do i change it?

Regards, Inger