How do I change my autofill information

Safari > Preferences > AutoFill

Click the Edit button next to Credit cards and edit the info.

Choose Safari > Preferences, then click AutoFill.

• To turn AutoFill off or on, select the information you want to include in AutoFill; deselect the rest.
• To change or delete AutoFill information, click Edit next to the information you want to change or delete

https://support.apple.com/guide/safari/use-autofill-ibrw1103/mac

I suspect a lot of that is in Contacts.