Wipe the base of the elf ear (where it joins onto the real ear) with a makeup sponge to clean any loosened makeup or liquid latex from the seam. Wipe the entire seam so that you can clearly see it.
Roll the seam of the elf ear away from the skin, using your fingertip, wherever the elf ear begins to roll up. Paint spirit gum underneath the loose prosthetic and press and hold to the skin for 10 seconds. Paint the spirit gum onto the prosthetic and not the skin, or it will not hold as well. There is a brush attached to the cap on the spirit gum to do this.
Pour liquid latex onto a clean makeup sponge and apply over the prosthetic elf ear and the skin. You want enough liquid latex on the seam so that you can no longer see it. Thin the latex out further onto the skin so there is no dramatic bump where the elf ear joins. Let the liquid latex dry for 15 minutes.
Use several clean makeup sponges to reapply the characters makeup; focus on matching the entire skin tone of the elf ear to the natural ear.