Canon EOS REBEL XS Instruction Manual page 72

Using the Remote Switch
Using the Eyepiece Cover
if you take a picture without looking at the viewfinder, light entering the
eyepiece can throw off the exposure. To prevent this, use the eyepiece
cover (p.22) attached to the camera strap.
Remove the eyecup.
® Push the bottom of the eyecup
upward.
_ Attaching the eyepiece cover.
® Slide the eyepiece cover down into
the eyepiece groove to attach it=
165