If your Salesforce instance changed, you have to change the configuration for the CTI Adapter URL.
To retrieve the new Salesforce instance proceed as explained in: my domain and change the CTI Adapter URL in the call center adapter
To make the change instantly available, the user has to logout and login again from Salesforce.
Do not change the Mirage Cloud Service URL as this would required to restart all TAPI Link / Skype for Business Connectors.
Additional help for all errors