How to change default notebook?

It seems I have designated one of my (eleven) notebooks as "default", though I don't remember doing that--or even how to do it.
If a default notebook is necessary, I would prefer it be a different one, but I don't know/remember how to make or change that designation.
Thanks,
D.G.

Look on the Annotate tab for the default notebook in the center.

Thanks, BowmanDH.
That was what I needed.

I was looking through the help section within the app for this as well as some other things (that I could not find), and its actually there, as well as other nice tips and tricks