How do I change my accounting method to CASH in QB Desktop 2020?

Hello, @lesliepurdy.

You can change the Accounting method in the reports when you are viewing or working on the report itself.

Here's how:

1. In the report, click the Customize Report.
2. Under the Report Basis section, select Cash.
3. Click OK.

See this article for more information: Understand reports. 

Let us know if there's anything that I can assist with. I'm always glad to help in any way I can. 

In QB, this is just a reporting preference.

You can change it on each report you run, or you can change the preference at Edit | Preferences | Reports & Graphs | Company Preferences | Summary Report Basis -> Cash.