You'll have to insert a section break; then you can change the orientation in the Page Setup dialog box. Or just select the text whose orientation you want to change and change the orientation. Word will insert the required section break(s) for you.

To display the Page Setup dialog box, click the dialog launcher button (the little arrow on the bottom right) of the Page Setup group on the Page Layout tab.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional