try checking the sd card (or whatever the app was on) on your computer, if its there, get a new download, it could have been corrupted. if its not there, same thing, new download. if that doesn't work then idk what to say, thats all i got unfortunately...

What did you install??? Your best bet is reinstalling the homebrew channel, you can probably find it somewhere on the wii u mod guide

i just installed a thing where the homebrew launcher would be there but in the wii u