Hi @Andrew_Taylor1,
Welcome to Airtable Community ! :grinning_face_with_big_eyes:
If you are the Owner of the Base, press on the small number on the upper right corner of the Base in your Workspace, a list of Collaborators will appear, you can then remove them as you wish.
If they are Workspace Collaborators or on several Bases, you can go to your Account, click on the Workspace on the left that you want to remove them from and you will find a list of your collaborators.
BR,
Mo
