I tried to practice coding QT3D in demo but i dont know How can i move timer.js to QML folder
First of all, don't use a picture that is so small. I can't see anything.
Anyway, the js files (if added by Qt Creator) will usually be in the qml folder by default. However in the Qt Creator Projects View it will look like it is in another folder. That is because Qt Creator differentiates between qml files and other files to simplify your work.
If your right-click the js file you can select from the context menu "Show in Explorer" on Windows or "Show Containing Folder" on Linux, this will allow you to see where the file is on the Hard Drive.