PCB123 will allow you to place the missing sections. Use the following steps from the schematic.
Right click on one of the existing sections of your multi-section symbol and select properties. Copy the _PARTNUMMFG Value then close the properties window.
Go to the toolbar and select the Add Part button. Paste the copied manufacturer’s part number into the search criteria then select Go. Locate the correct part in the list of parts then select OK.
The missing section of the schematic symbol should now be attached to your mouse. Left click to drop the section.
Repeat these steps for each missing section of a multi-section symbol.