There two ways for setting custom attributes for contacts
1. Set attributes via SDK method
To set a contact custom attributes call setCustomAttributes method as follows,
2. Set attributes via contact side panel
After creating contact custom attribute, you will be able to add these attribute to the contact via conversation/contact sidebar.
It will open a attribute dropdown selector, then select the attribute that you want to add
Enter a valid value, click on the Create button. If the request is successful, a message “Attribute added successfully” will be displayed.
Also you could able see the actions like edit/delete/copy by hovering on the attribute.