Installation help ... chrome crostini w/ arm processor

Can I post a screenshot here? I am a linux newbie, trying to install Musescore on a chromebook with an arm processor. First off, the terminal asked me for a password, which I don’t have since I just installed this Crostini thing and it never asked me to create a password. So I googled around and figured out how to switch to root and create a password there (but please, can you tell me how to get out of root? and how to figure out or reset my password as end user?). Anyway, I tried to run the app, and the terminal said “This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.” I tried repeating the install command, but it failed because the app is already installed. I don’t know how to uninstall it and try again.

Linux for dummies? I know NOTHING! Thank you all for being here.