Customer notification email is sent automatically for Wishlist reminder and Product low in stock. There isn't a way to manually send a customer notification Email. If having any issue in sending customer notification, please email us at firstname.lastname@example.org . We will check why the email hasn't been sent out for you.
There's no need to re-install the app when changing or updating a theme. You need to update or adjust some settings as In the admin console, go to Online Store > theme > Choose the theme > Click on Action & Publish > Go to MyWishlist App Dashboard > Check setting is Enable > Go to Button design menu > Save Setting. If having any issue with this, please email us at email@example.com