OK, I have received the document. It has a continuous section break a bit above the middle of the first page, which is actually the only page. When you change the bottom margin, this affects the first section. Temporarily add a page break (or just press Enter repeatedly to get onto the second page); then you can change the margin there, for section 2.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional