Making new Div id's / alter HTML

CMS & WordPress
1

Hi

I am working on a site and have a child theme to add my css code.

I have found I want to make a new Div id, but I am unsure on how to edit the Html is it is generated from PHP. I can’t send a link to the site as I am working offline.

Do I go into the header php file to make the change?

Please help me figure this out.

Regards,

2

It depends where this div should be.

3

It needs to be within a page.

Should there be a conditional statement or something, if page 44, use this?

4

No. For this special page you can make template page that will be used:
Pages « WordPress Codex