Reimport Accounts with reference to Contact

HI,

we use a Primary Contact in Accounts.

With the Data Migration Wizard i imported Accounts first, then Contacts.
The relation works fine.

Now i must update Accounts with a reference to the unique Contact-ID.

I know update is possible with " Import My Organization Accounts", but then i have no reference.

Data Migration Wizard makes no update, but makes a duplicate.

Any Solution?

Hubert