GarageBand for Mac

Did you delete your version 6? Usually the GarageBand 10 installer will move the old GarageBand application to a subfolder of applacitions. You should find it in the folder Applications > GarageBand 6.0.5 and it works well with the library installed by GarageBand 10. you can keep both versions for different purposes.

Otherwise restore the GarageBand 6.0.5 application from your TimeMachine backup, if that does include your Applications folder.

Is there a way to get it back to launchpad.

if you add an application to the "Applications" folder, it show up automatically in the Launchpad. It should show up even in its subfolder. If you do not see it there, try to drag it to a folder outside the Applications folder and then put it back there.