The official advice there involves wiping all recordings by doing a factory reset via the box menus . Recordings can be preserved if performing a factory reset keeping recordings (using the box Pro reset button NOT the menu) as described in https://www.bt.com/help/tv/fix-a-problem/tv-boxes/how-do-i-reset-my-bt-tv-box- (click on the box pro image to see the reset using button instructions) So if you have no aerial connected to the box before you start the factory reset (keeping recordings) you get the Ip Mode setup. If you have a functioning aerial connected you get aerial mode. Haven’t personally gone through this process for a while.
Note that if your box in aerial mode any freetoair Recordings made whilst previously IP mode will not be playable.
