My razer sharp wit is sometimes wasted.
Tiger is replacing Kiowa, thus it will be going to 1 Avn Regt. Therefore, aircrew at 1 Avn Regt will be converted. That is not to say there might be the odd ex Blackhawk pilot piloting a tiger.
The converse is true of MRH90. It is going to 5 Avn Regt, thus it will be 5 Avn Regt folk transitioning onto the aircraft. I am leaving Navy aside here.
As ab initio pilots graduate, they also will be transitioned.