The only beetroot soup recipe I have uses fresh beetroot, but am sure the pre cooked stuff will be fine.
Basically, boil it up (perhaps not necessary w pre-cooked), retain cooking liquid for thinning the soup, blitz the beetroot with a tablespoon of dijon mustard and a tablespoon of balsamic vinegar. Can thin with cooking liquid. Add sour cream as garnish when serving.
Think this might be a "How To Eat" recipe rom Nigella (can't remember). Easy peasy.
i used to make beetroot soup with cooked down tomato and stock. then add some feta right at the end when you dish it up (a few cubes of salty cheese goes lovely with sweetness of the beetroot). watch your wee though