..hi have a good day! I accidentally deleted my garageband project..how to retrieve them back?thanks

Did you check if it is still in the trash can? If it's still there you can select it (right click) and choose "put back".

There is data recovery, but the kind that would have the best luck in grabbing a project "file" (which is actually a bunch of files together in one) generally run about $80, although you can try them out for free to confirm that it claims it can restore it:

EaseUs and Stellar are two good ones.

PhotoRec is 100% free, but I'm almost positive it wouldn't help in your case with a project file as it only deals with individual graphics/doc/etc. files.

You have to go to "Account Settings" on the www.icloud.com web page to see the "Advance" section that has the "Restore Files" link, at least on a computer browser that's how it is. Not sure if this works the same (or works at all) on iOS.