how to "un-tick" boxes on tasks?

I started using some tasks in the binder ala’ snowflake method.
However I can’t seem to to un-tick the boxes - they seem to be created with the “ticks” already done.
I would obviously like to be able to tick the tasks as I go but I can’t seem to do this.
What am I missing?

That is an icon not a checkbox. Right-click on the icon to change it to something else if you wish to use icons as status indicators. As for this icon, it wasn’t mean to be a status indicator, just something to let you know that document is or contains something “to do”.

thanks amber
I just use a “star” now for completed “to do” tasks.