Hi
Biggles - welcome to the forum!
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!