Turn on the Advanced Toolbar.
View the Contacts folder in the Phone List View.
Turn on the Group By Box (from the Advanced Toolbar)
Drag the column header "Company" into the Group By Box - it's a grey box
that appears when you click the button on the Advanced Toolbar.
Make the correction to one of the Contacts so the Company name is correct.
That 1 Contact will be in a group of its own.
Select and drag all the Contact in the old Company Name group into the Group
with te right one.

Regards

Judy Gleeson
MVP Outlook
Trainer and Consultant

There are various articles about using Outlook here:
www.judygleeson.com/articles.aspx
Canberra, Australia

"What do we live for, if it is not to make life less difficult for each
other?"
George Eliot