A320nx V6 speed on approach won’t slow down

You should learn how to use all the Managed and Selected options in the FCU. If you find yourself too fast on approach you can … (because setup was not completed)
Leave Throttle on Climb … then On the FCU set Speed Selected Mode and set to 200 (on keep speed below 210 direction) (gear down and flap 1) then down to 120 (or whatever increasing flaps until full) and move throttle to Idle & flare 20-30 feet