Navigate to the Control Panel > Services Tab > Setup Section > Service Providers.
Use the search panel to find the volunteer, then click the Additional Contacts icon in the Maintain Column.
Hover over the icon to reveal the icon's name as a tooltip.
If you're using Volunteer Self-Signup, volunteers can manage their Contacts from the VSS screen (see About Volunteer Self-Signup).
Enter additional contacts for the service provider, such as another family member or trusted friend. Additionally, if the service provider is a secondary or tertiary member, you will see a button "Copy Primary's Contacts". Select the button to copy any Additional Contacts from the primary member to the secondary/tertiary member.