Withdrawing an invitation blocks a user from being able to complete a qualification, stops them appearing in your Worker Group(s) and blocks them from seeing other users if they are a manager or administrator.
Simply go to the Users list under Invitations and find the user you would like to withdraw the invitation from.
Click on the 3 dots under actions:
You will then see a list of action items - select Withdraw:
To withdraw an invitation from multiple users at once, click on the tick box next to their invitation:
Click the Withdraw icon to withdraw the invitations from selected users: