How can i export my project to imovie file for another people to edit my project

You cannot "export" a project other than in Mp4 format. Projects cannot exist independently but must reside in an iMovie library. So, to transfer an editable project you would need to transfer the library that contains the project.

This is usually done by copying the library to an external thumb drive that is formatted Mac OS Extended (Journaled) and then physically transferring the thumb drive to another Mac computer (must be a Mac) that is running the same exact version of iMovie (very important) that was used to create the project. Before copying over the library, select its name in the iMove sidebar and do an Edit/Consolidate Library Media. Also select the project icon in the project browser and do an Edit/Consolidate project media. For convenience, copy over the project to a newly created library so that the library you are working with contains only that one project.

Another possibility is to Air Drop the library to another Mac computer that is running the same exact version of iMovie. I have only tried this once, myself, and it seemed to work fine. Haven't experimented sufficiently with it to fully check it out.

A third possibility is to export as an Mp4 file and transfer the Mp4 file to your third party collaborators. They could then import the Mp4 into an iMovie project and do some limited editing, such as splitting and rearranging or deleting segments, adding titles, adding music, and so on. Edits already embedded in the clip could not be changed.

As a caveat, always separately back up your original library, and use "copy" rather than transfer, so that if anything goes wrong you still have your original work. Also for safety, wouldn't hurt to keep an exported Mp4 as a backup.

-- Rich