As an administrator you can associate users with companies in bulk. Only the companies available to the administrator can be used for this feature.
Associate Users with Companies
Settings, Users
Select the desired user(s) by ticking the box before them
Select the Bulk Change button
Select Properties tab
Navigate to Available Companies, 'Select an option'
Choose one of the options: Add, Replace all, Find and remove, Remove all
A second block will appear, except if Remove all was chosen. Click on it
A list of all the companies you have access to will be displayed
Select the desired company(s)
Click on the Apply button at the bottom of the sidebar
Change a User's Default Company
Settings, Users
Select the desired user(s) by ticking the box before them
Select the Bulk Change button
Select Properties tab
Navigate to Company, 'Select an option'
Select Replace
A second block will appear, click on it
A list of all the companies you have access to will be displayed
Select the desired company. Only one company can be selected as primary company
Click on the Apply button at the bottom of the sidebar
If a user only has access to one company and you change the default company to another company in your instance, the old default company will be added to the user's available companies list. You will need to remove this company from the user's available company list to ensure the user does not have access to that old default company.