Welcome to Android Central! This is the problem with using stock note-taking apps that don't sync anywhere automatically -- if you lose a note, it's often not recoverable. In the future, I strongly recommend using an app like Google Keep Notes or Evernote.
Which phone do you have? Use your file manager app to look for a directory that might contain your note files. (This might not be possible, since the app might save this information in a protected system directory -- I don't know for sure, since I don't have an LG phone.)
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