warming soup on shabbos

Question

Rabbi, if you would please clarify something since i've heard a few different opinions. In one post a reader asked if they can put soup on a blech if the blech was on timer to go on after the soup was put on the blech, and another post said you cannot heat up liquids. Can I reheat soup in a warmer on shabbos? The warmer is plugged in before shabbos and just has one temp. setting? Would it change if i put the warmer on a timer to go on after the soup was put in the warmer? Thank you very much