Well, contact the developers of mobile applications. I know professionals who can create an event application for you https://giraffestudioapps.com/offer/android-mobile-apps/event-app-development/ which will also contain all the functions you need. But it costs a lot of money. Are you ready to invest them? And how exactly do you plan to attract people who are not indifferent to animals? After all, they must somehow find out about this application too. Is not it?