Navigate to Appearances → Menus to manage the navigation of menus and order of menu as you prefer.
Select the Pages you want to add to the Menu under the Menu structure.
You can also add the Custom Link to the Menu.
Select and add the Salesforce Portal modules/submodules for the customer portal option. Select the modules and by clicking on the Add to Menu button the selected modules will be added on the right side under the Menu structure.
Under the Menu structure, you can manage the menu & its submenu by dragging up-down any menu to change the order of the inserted menu.
From here, you will get the Custom Object, if you have enabled from the CRM.
After changes, click on the Save Menu button to save all the Menu item changes.
Note: if any new object is enabled/disable from the CRM side, you can add to the menu manually.
Delete the menu and navigate to the ‘Customer Portal’ settings menu, the Menu will be recreated. You can select the Menu location and Salesforce Menu.
After managing the menu, click on the Save Menu button.