Not sure I get the question. Basically it is in a row A - B - C so B is in between A and C. It is not separate piers. Simply get off the train at B gates then when announced get back on the same train for B going to C.

Other choice is to walk, there is a great guide here on how to do it. Just take the elevator to the lowest level. I have done the walk with my two boys since they were five. Something different and fun and gets some exercise in us.

(As was posted you will need to know the walking route back in case you are from A10, very unlikely but be prepared as you cannot take the train back). You will get plenty of notice, just watch the boards.

Ignore all the signs on the boards when A gates to wait. Just go straight to B to enjoy a good lounge. You can also order champagne from the staff if that is your preference. Spa I think has less of a queue as well.

KF