LectureNotes can store your notes in the extSdCard directory. You need the app to point to that specific location though. To do this, open LectureNotes and press the 3 vertical dots stacked on top of each other. Select 'Settings'. On the left pane, select 'Storage'.
Under 'Directories', select 'App directory setup'. Select the third radio and change the directory to: /storage/extSdCard/LectureNotes -->Note, the external card directory is CASE SENSITIVE. It has to be extSdCard exactly. Press 'OK'. Close and restart LectureNotes. All notes now will be stored in the external card.
Now comes the tricky part, relocating your old notes to the new directory. It didn't relocate them when I changed the directory path. All your old notes are located in: sdcard/Android/data/com.acadoid.lecturenotes/files. Move only the notebook folders over to the extSdCard/LectureNotes directory. But if you don't know what you're doing, make a copy instead of a move that way you have a backup to go to just in case. If you moved all your notes from the internal storage to the external one, you an safely delete the com.acadoid.lecturenotes directory. Make sure there are no files in the directories before deleting them though.
Everything should work as stated as that is what I did and took me a while to figure out what to do to get the old notes over to the directory and recognized by the app.
