From the Custom UI portal (https://ip/vcops-custom) and with admin rights, go to de ADMIN tab and select SECURITY.
Create a new Accoun Group first and after a User Account as shown below:
Once we have the Group and the User, it´s time to assign access to the custom dashboard.
Go to the HOME tab, select the dashboard and click on SHARE:
Select the dashboard that you want to share and "drag-an-drop" to the Group (from the right pane to the left pane).
Let´s go to test it! Open the Custom UI portal with the credentials of the new user and verify that this user only have access to the specific custom dashboard: