To modify heading numbering, do the following: Place the insertion point in the first level 1 paragraph of the document (meaning the first Heading 1 paragraph in this case). On the Home tab, click Multilevel List, and then click Define New Multilevel List (note that the command label is misleading). In the dialog box, click the More button to see all options. Change the "Start at" value for level 7/Heading 7 as desired, and then click OK. Note that this changes the number for the first level 7 item in the document, and the others will follow. If you are trying to do something else, please post back.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional