Within Teamwork Desk, you can choose to
    enable or disable individual custom fields at
    anytime.
Note: Custom fields are available on Premium subscriptions and above.
To do this, click your profile icon
        to the top right of the navigation bar and
        select Settings.

In the settings area, go to the General tab.
Note: Only site administrators can
    access and update custom fields.

In the left pane select Custom Fields.

You will then be presented with a list of
        your existing custom fields.
To enable an existing custom field,
        toggle on (green) the option in the
        Enabled column.

To edit the settings for an existing
    custom field, hover over it and select the
    edit pencil.

To remove a custom field entirely,
    hover over it and select the trash can icon to
    delete it.

For more information, see: Adding a New Custom Field