I managed to get it installed.
I could find no instructions on how to enable this, so I will share:
Click on the “File” tab, In the new window that opens, click on “Account” near the bottom left corner.
In the new window find “Account Privacy” just below your user information on the top left.
Click on the “Manage Settings” button. A new privacy window opens.
Select the “Turn on optional connected experiences” check box near the bottom of the window.
Click the “OK” button in the bottom right corner.
You will need to re-start Office for this change to take effect.
I went here:
Clicking “Open in Excel” eventually started Excel to begin the character registration process.
Selecting add-ins now looks like this:
