1
Open the Settings App, then go to Apps & features, scroll down the list of installed apps, do you find Microsoft Office listed there?
If you do, the best option is to full repair of your Office installation.
Select Office and choose Modify - Online Repair.
That should fix any issues with your Office Installation.
2
If you do not find Office in the list of installed Apps, then go to your Microsoft Account on this link to re-install Office on your PC.