you shouldn't have to relink because main board has nothing to do with communication with the controller. it's all in the OFDM.
but if you need to:
turn both on,
click the bind button on the phantom - small white box under the phantom has a light and a small button on one side of it, use small screwdriver / toothpick and press and hold the button untill light starts blinking red,
now on the controller (you don't need to be connected to the phone / app) at the same time press C1, C2 (two white buttons on the bottom of the controller) AND record button on top left for two seconds,
you will hear D-DD,
release,
press right wheel on top right in for two seconds,
you will hear controller beeping.