How to Manually clear the Excel Add-in Cache

Here is a link to the Microsoft Documentation.

https://learn.microsoft.com/en-us/office/dev/add-ins/testing/clear-cache

But here is an extract of the important steps, incase Microsoft move or delete that page.

Clear the Excel Add-in cache on Windows

To remove all sideloaded add-ins from Excel, delete the contents of the following folder.

%LOCALAPPDATA%\Microsoft\Office\16.0\Wef\

If the following folder exists, delete its contents too.

%userprofile%\AppData\Local\Packages\Microsoft.Win32WebViewHost_cw5n1h2txyewy\AC\#!123\INetCache\

Clear the Excel Add-in cache on Mac

To remove all sideloaded add-ins from Excel, delete the contents of the following folder.

Note: To look for these folders via Finder, you must set Finder to show hidden files. 

Finder displays the folders inside the Containers directory by product name, such as Microsoft Excel instead of com.microsoft.Excel.

~/Library/Containers/com.Microsoft.OsfWebHost/Data/

If that folder doesn't exist, check for the following folders via terminal and if found, delete the contents of the folder.

~/Library/Containers/com.microsoft.Excel/Data/Library/Caches/

~/Library/Containers/com.microsoft.Excel/Data/Library/Application Support/Microsoft/Office/16.0/Wef/

~/Library/Containers/com.microsoft.Office365ServiceV2/Data/Caches/com.microsoft.Office365ServiceV2/

~/Library/Containers/com.microsoft.Office365ServiceV2/Data/Library/Caches/com.microsoft.Office365ServiceV2/