You have Office 365 already. You should upgrade from Office 365 to Office 2019 instead of Install stand alone Office 2019.
Control Panel, uninstall office 2019.
Office 365, update, it should update to Office 2019 (work in Windows 10 only). No need to do activation again.
It will become Office 365 base Office 2019 version. You still will get all future version Office update and new feature update as well.