Open Clean a scan from the Home screen (or use its own page link).
Tap Choose files and select all the files you need (you can select several at once).
Choose a look: Auto clean (best) gives white paper and sharp text; Keep colours keeps colours; Grey and Black & white make smaller files and print well.
Optional: tick Make searchable (OCR, English) so you can search and copy text in the result.
Tap the big purple Start button and wait a few seconds.
When you see Done!, tap Download. The new file is saved on your phone or computer.