Changing numbering in a Heading style

[TheQueenBea]

I am working with a document I did not create and it is a stand-alone chapter of a larger document. The TOC and all pagination, including the front matter footer, starts with a 12. I need it to start with 13. Looking through all the custom styles, I have found that the Heading 7 style is where it shows that the numbering should start at 12. I have not found a way to modify that to be 13. When I click on Modify Style, then Format Numbering, it does not give me an option to change the start number. Is there a way to do this? Thanks in advance.