Not sure from your description whether the blue pins have stopped working for you on the maps app or whether you need to delete them?
But just as a starter, I would suggest that you double-press the 'home button' - the taskbar should open at the bottom of the screen - find & hold the maps app - all icons should start to jiggle; on the map apps press the x in the left upper corner; this will close down the maps program - then try a re-start from your home screen.
If this is not successful, then try to restart or reset (in that order) your iPad - directions HERE - if none of these maneuvers solve your problem, then please re-post and better explain what you want to do w/ this app - good luck!