Hwo can I save the registered .nii file in ITK-SNAP

Question

When I use ITK-SNAP,after rigid registration,I want to save the .nii file.But when I use the button save(in the picture),the .nii file is same as itself before registration. So I want to know how to save this .nii after registration.the "save" button

So I want to know how to save this .nii after registration.