Hi,
To add more, you can make a common change to all contacts in the following way:
1- Open the folder where contacts are stored
2- Use view menu
3- Select Customize View dialog box
4- Use 'Group By' option to click, a dialog box appears, you can change the required contacts.

I want to add one more additional tip i.e., sometimes it is seen that Outlook contacts may get damaged. In this situation, it is required to opt for Outlook contact repair tool. You can read more detail at:
http://www.stellaroutlooktools.com/scan/recover-contacts.php

Regards :
Russell