If you want to install or reinstall office 365 or office 2016 for mac, then follow the step by step process for it:
How to Install Office 365 or Office 2016 for MAC?
Sign in and install Office by visiting https://setup.office.com/ & follow the instructions.
Enter your product key to redeem your product.
The my Account page will be opened where you will see a button of Install.
Click on Install.
A Page will be opened containing the install information. Click again on install.
After the completion of download, open Finder & go to downloads.
Click on Microsoft_Office_2016_Installer.pkg
On the next page click on Continue to begin the installation.
Click continue on the software license agreement.
Click on agree to the terms & conditions.
If it is asked to enter the MAC password then enter it to install the software.
After the installation is finished, close that page.
for more details, visit : office.com/setup