When an employee has left your company, you will want to reflect this in their Breathe profile.
To do this go to their profile > edit (pencil icon) > change person status:
From here you can change their status to pending, current, leaving and left.
Below is a tutorial on how to action this within your Breathe account.
PLEASE NOTE: You must enter a leave date as you will be unable to complete this action without this.
When you mark someone as having left your company, this will block their access to their Breathe profile.
I don't see the option to mark them as 'Left'?
This will most likely be because the person is the Admin on the account. They will need to transfer those rights to another HR user (via their own login) before you can register them as a leaver.