There are 3 ways to open a CSV file
Open a new file
Touch the Plus button on the right corner of the main screen.
For the first touch, the below pop-up will appear. Choose Allow to let the app accesses files on your device. If you choose Deny, you must change it again in the device setting.
Open Recent files on the Home screen
Once opened, the CSV file will be saved automatically on the Home screen. Now you can open it again whenever you need to.
Open a new file directly from File Manager on your device.
Open Files → choose a CSV file → open with Smart CSV: CSV File Viewer.