You must be an account administrator
Go to settings. Click on your name and/or avatar and choose settings from the menu
Select User Management followed by Users
Locate the user in the list of active users and click on the envelope icon next to the red 'not yet activated' message in the Account Status column.
Click the Copy Activation button to copy and send from your own email account, or click the Send Activation Email button.
BaseBuilders Knowledge Base
Account and User Administration
User Management Activation Email
Sending invitation emails to new or existing users. Click your name/avatar at the bottom of the main navigation panel to open settings.