Daylio opens CSV in a wrong app
We suggest using the storage apps like Dropbox, Google Drive or email apps, so you can easily send CSV file anywhere.
If you somehow set up a wrong default app for opening CSV file you can always change it in the Android settings. Just go to Android Settings > Apps > "App name" and tap on the button CLEAR DEFAULTS. Remember you need to go the app that is opening the CSV files, not Daylio.
Next time you click export it will ask you again to choose app to open CSV.