Golum, I rewound that roller blind as you said,
if you have lazy rewind on these its a five minute job,
small phillips screwdriver (preferably magentized tip)
small torch
Pop off the window surround, its in four pieces, that just click on and off clips around window, unscrew the three screws in (right) sides slide
unscrew the (right hand end of the roller blind only) and pull blind out sideways,
use the white plastic block that holds the roller blind in to re-tension the blind (15 turns I made it)
pop it back in place and secure with both its tiny screws,
replace the right hand slider (3 screws) might need to clip both blinds together for this
and pop the surround back on
not really worth pictures this one, but if you need them I'll go and take some