Need help creating an alternate header/menu for a collection on my site; Dawn theme

[JillKn]

WHAT I NEED: I need help creating an alternate header/menu for a collection on my site. I've gotten as far as understanding that I need to edit my theme.liquid file.

WHAT I'VE DONE: I have created the alternate menu and saved it.

WHAT I'VE TRIED: So far I know how to edit the theme for a collection: Online Store > Themes > Customize > Then in top middle tab, select Collections > Create Template. When I'm in create template, I adjust the header according to what I want that collection's header to look like. But then those changes are applied across the entire site. 

WHAT I KNOW: I understand that I need to assign header collection within my theme.liquid file to solve this problem, I just don't know where to create and how to call the second header group. 

WHAT I NEED: Can anyone 1) Help me solve this on my own, or 2) Teach me for a fee. 

Please help! Site is https://www.bennetttothetrade.com/; Collection is https://www.bennetttothetrade.com/collections/pewter.