Hi Ying

The project manager and project followers will automatically be added to the list of followers for the tasks/new tasks in that project.

If you have the rights, edit the Project followers, going through "Edit" >

and setting the followers at the bottom on the right >

You can delete followers with "x" or edit the "subscription/shared posts" for them by clicking on the "pencil"

If necessary, you can also set the followers in each task independently, in the same way.

BR

Ricardo