On a desktop or laptop machine login to your Google account and open New Chartroom in a browser such as Google Chrome.
Go menu File > Make a copy... and give it a name.
That's it. You're done.
A Chartroom spreadsheet comes fully-configured with all the software it needs to operate.
At all times you are the owner of your data. At various points you will be required to allow Google to run Chartroom software against your data. If you are happy to allow this then click Allow when these authorisation requests pop up.
Google Sheets saves your work automatically, and periodically takes snapshots of the entire spreadsheet in the Revision History.
Chartroom's primary user interface is via a web browser and this may be all that you ever want to use. But once your charts have been created you can use the Google Sheets app on a mobile device to enter scores and run through to completion.
Like any work in progress there will be times when you want to go back. Firstly try Ctrl+Z Undo. If this is ineffective, and if the problem is serious enough, you can restore the whole spreadsheet in the Revision History (Ctrl+Alt+Shift+H).