You can change the size of all icons in Windows by choosing some other display option in File Explorer. In a folder, right-click and choose View from the context menu; then choose the option you prefer.
Since the Office update changed the icons, you can't revert unless you uninstall the update. That is not a good idea, though. For security reasons, you should always have the most recent version of Office installed.
Maybe there is some Windows "hack" you can use to customize the icons. I am not sure. It would be better to ask in the Windows forum.
Long-term, I suggest that you send feedback to Microsoft, for example via the portal at https://feedbackportal.microsoft.com/feedback/forum/fb6d67e3-301c-ec11-b6e7-0022481f8472 .