First, to make sure the WeddingMix App wasn’t accidentally deleted, try to install again in the App Store.
If the WeddingMix App screen shows a blue "OPEN" button, then the WeddingMix App should be installed on your device and you just need to find it.
There are two ways to find any app you're missing on an iOS device such as the iPhone. In both cases, start from the home screen by pressing the main round "Home" button.
1) "Swipe" with your finger, screen by screen, until you find the WeddingMix App. Make sure to check each folder (the icons that have other smaller icons in them) on your device.
Once you find the WeddingMix App, you can move it wherever you like. To move an app, touch and hold the icon with your fingertip until it "wiggles"-- then drag it where you'd like it to go.
2) Or, "pull down" from any screen with apps to reach the iPhone "search" screen. Then search for the word "WeddingMix." You still won't know where the app actually landed using this method, but you can still launch the WeddingMix App this way.