How to change entry point for customers and use a special URL to access the panel, such as panel.example.com?
First of all Brand has to be created at Provider panel > System > Brands > Create new brand. Please refer to the corresponding chapter of the Plesk Automation Branding Guide
After the brand is created, the domain name specified on brand creation can be used for access to both provider and customer panels without specifying port
Furthermore, branding enables hosting providers and their resellers to change the look of the user interface they provide to their customers. Several brands can be created if needed:
https://172.16.10.15:8443 -- this is address of management node https://panel.example1.com -- this is a branding URL 1 https://mycompany.example2.com -- this is a branding URL 2
More information can be found at Plesk Automation Branding Guide
Also, refer to the following chapter of the documentation to learn how to change the visual appearance of the control panels: