To fill in missing eyelashes, you can opt for various methods. One popular option is using false eyelashes, which can be easily applied and give the appearance of fuller lashes. Another option is eyelash extensions, where individual extensions are glued onto your existing lashes to add length and volume. If you prefer a more natural solution, you can try lash serums or growth enhancers that stimulate lash growth and make them appear fuller over time. Mascara is also a quick fix to temporarily add volume and length to your lashes. Lastly, consider maintaining a healthy lifestyle and proper eyelash hygiene to ensure the overall health and growth of your lashes.