how do i change the copywrite to say something else

The copyright text (not copywrite by the way; it is the right to control copies) in the footer is picked up from the project properties using the meta tag $c or $C. Edit the copyright text in the Project properties.

See https://musescore.org/en/handbook/4/setting-your-score and in particular https://musescore.org/en/handbook/4/setting-your-score#title