I did this a few years ago using a free screen recorder. Since then applications have moved on, so I googled for the latest info. Here is a list of the best FREE screen recorders in 2019. Note that many are designed to be fast for gamers to demonstrate their skills. You do not need this type of recorder, just a good quality normal speed recoder will do for Excel.
https://www.techradar.com/uk/news/the-best-free-screen-recorder
If it were me, I would use the third one Apowersoft Free Online Screen Recorder because it is on line, you are not installing an app, you do download a toolbar to allow you to use it.
Note DO NOT DOWNLOAD the 'Download desktop version'as this is only a demo of a paid for version. Just click the start recording button and that will link to your control panel download for the free on line version.