If there is backed up files, recover them is easy. If you haven't backed them up before, you could try Android data recovery program, such as MobiKin Doctor for Android, it will detect the internal storage and extract the deleted data.

NOTE: For a guide on how to back up data on the phone, check this thread.

Restore App Data:

1. Open “Settings”
2. Access “Phone Management”
3. Tap “Backup & Reset”
4. Tap “Restore from backup” and select the desired backup file
5. When ready, tap “Start” > “Done”

NOTE: You might need to reboot the phone to complete the process.

Restore Contacts:

1. Launch “Settings”
2. Access “Phone Management”
3. Tap “Backup & Reset”
4. Select “Restore from backup” under “LG Backup”
5. Select the desired backup file and tap “Start” > “Done”

Restore Media Files:

1. Open “Settings”
2. Access “Phone Management”
3. Tap “Backup & Reset”
4. Tap “Restore from backup” and select the media files you want to restore
5. Tap “Start” > “Restart”

Restore Media Files from a PC:

1. Connect the Android phone to the PC via USB
2. On the phone, enable “File Transfer” / “Media device” at the prompt or from the Notification area
3. Open the File Explorer on the computer
4. Navigate to the media backup files on the PC
5. Copy and transfer the files to the phone storage, preferably in the folders of origin
6. Once done, eject the phone storage and safely disconnect the device from the USB port