To switch the company connected to your LinkedIn account in Expandi you should first create a new company.
Click the user name on the top right hand corner
Select Add a new company
Enter the company name
Enter the agency you wish to connect it to
Then you should go to the Profile Settings via the dashboard
Select the tab on the left which says Switch LinkedIn account Company
Search the drop down list to find the company you wish to change to. If you don't see it you should click the Sync LinkedIn Account button, which is on the top right hand corner
Click the button which says switch
Your company should now be successfully changed.