It happens. For whatever reason your culture gets contaminated and you need to remove vessels or wells from your culture track.
Create an action group with the vessel/wells that are contaminated.
Change the action display from 'Today's Actions' to 'New Actions'
Select 'Terminate'
The platform present a modal with a drop down menu a list of 5 possible reasons for terminating the culture.
You can select one or click on the 'I don't want to add a reason now' link.