You can't. Autocompletion does not use your Contacts. It uses a cache of
names from messages you have sent. You can populate that cache all at once
if you want:

In MS Outlook, go to tools, options, mail setup, send/receive.  Uncheck the
"Send immediately when connected box".  Next, press the Send/Receive Button
(in Options) and uncheck "Schedule an automatic send/receive". Finally,
click "Work Offline, or if you want to be extra careful, disconnect your
computer from the internet by removing your network and/or telephone
connection.

Now open a new e-mail, press the bcc or to or cc button, select the contact
folder you would like to bring into your NK2 (autocomplete) file.  Select
all names by highlighting first and last contact and then add them by
pressing the OK button at the bottom.  With your computer disconnected from
your mail server, press the send button.  This will automatically populate
your autocomplete file with all of the selected e-mail addresses.  Next, go
to your Outbox and delete the e-mail(s) that you just created.  Go back into
your Tools, Options, Mail Setup, Send/Receive and change your options back
to the original settings.   Remember to put your mail settings back and plug
in your removed cables.