I’m assuming this is an app on your current phone? In which case it’s an Android or IOS app, and won’t run on the Librem. Generally speaking: whatever apps you have on your phone today won’t run on your Librem. You may have equivalents for general purpose stuff, e.g. you’ll have a browser and an email client, but no Google Sky Map, and perhaps more importantly, no banking app.
For a couple of apps you could work around this issue using their mobile websites instead. But not everything has a mobile website, so some stuff will not work. Be sure that this is something acceptable before you make the switch, and also check @amosbatto’s link to the list of apps in development to get an idea of whether there’s at least an equivalent to something you depend on.