Wix Studio: how do I access the 'create new password' pop-up?

I’m having trouble accessing the ‘create new password’ pop-up and the resulting ‘you’re all set… login’ pop-up.
‘Create new password’ appears in the Site Pages list, but if I select it nothing appears, so there’s nothing to click/select and change/reformat (yet the ‘Login’ and ‘Reset Password’ pop-ups, for example, do open and I’ve been able to format every element).
3 dots (…) displays only ‘Rename’ and ‘Settings’; the latter only lets me change the PAGE background colour, not the pop-up and makes no difference at all.

And I have absolutely no idea how I would access and reformat the resulting ’ You’re all set’ pop-up with the ‘Login’ button - I only discovered it through testing.

Any help would be truly appreciated. Thank in advance

Ruth