Orient the lever so its clip is aligned with the arms of the spring.

Move the lever toward the camera, making sure the clip is compressing the spring.

While compressing the spring, slide the middle of the lever over its cutout on the camera until it snaps into place.

This can be a little tricky, as you have to constantly compress the spring while aligning the cutout. Work slowly and avoid moving the lever horizontally to prevent the spring from ejecting.