Export band values as CSV

Hello, I’m trying to export some calculated band (specifically, B3B2) raster values in a CSV file, preferably in some specified locations. File → Export → CSV → Subset (button) → Band subset (tab) → Select none → Select B3B2
shows Estimated raw storage size of 0 Mb. Indeed, the saved file does not have anything.
Only if I choose original bands like B2 something is being saved. Coordinates in this case are pixels. What should be done to change them to lat-lon or UTM?
What am I doing wrong? Would be grateful for hints or pointers to useful manuals (couldn’t find any yet).
If anybody can suggest a way to import the locations from where values would be exported later, it would be even more helpful.
Thank you in advance.