How do you fix an unknown command in AutoCAD?

I don’t know how to fix an unknown command in AutoCAD

Perform the following steps in the order listed: Open the drawing file. Purge Registered Applications (from the command line): Type -PURGE. Type PURGE at the command line. With all checkboxes checked on, click Purge All. Audit and fix any errors: Type AUDIT at the command line. Save the drawing.