Window-shades and blinds cannot be put up initially on Shabbos. If one’s blinds or shades fall one should not put them back up as this may be a form of boneh. According to some poskim, blinds or shades that can easily be slipped in and out of a bracket. The preferable approach, if one needs privacy, would be to take a towel/ sheet/ blanket and drape it over the pole/ tuck it into the bracket holder. As long as the intent is for this to temporary it is permissible.