I build a pedometer app, audio note app and now it got missing
Welcome Murtuza..
App Inventor automatically saves your Project every five seconds or so.
How do you know the Projects are missing? Are you using the main App Inventor server or https.code.appinventor.mit.edu/
Missing projects are almost always from logging in with a different Google address. This might be because you changed it yourself or because your institution changed their address