You first need to add a section break to the page you want to add the different margins to. Place the cursor in the page you want to insert the section.
Select Insert → Page Break → Section Break → Next Page to divide your document into sections.
Each section can have its own unique margin settings.
With the cursor in the target section, go to Page Setup → Margins.
Choose a preset margin (e.g., Normal, Wide, Narrow) or select Custom Margins to define specific values.
These settings now apply only to the current section, preserving the layout of the rest of your document.