As pp said I used to get bub into position on a pillow in my lap then hold the shield in place until she had got some good suction going.
The thing that got us off the shields was an amazing private LC who uses baby led attachment. I don't know how to explain but you basically just put bub on your chest & let them root around & carry on until they latch on themselves - none of the shoving them at your boob like some midwives in hospital did to me too! Couple of days of doing this (bit of a PITA cos you have to be patient), now she latches on anywhere anytime. I would highly recommend if you can find a good LC in your area & can afford it.