It's not worth the bother, Katie.
But anyway: The original screens have two metal frames, one inside the other. The edges of the outer frame are bent over the edges of the inner frame, and you will have to bend those sides back again. Doing so, you risk breaking the (cover) glass contained in most Hasselblad screens. But should you get lucky, you can take the two frames apart, and take the screen assembly out and replace it with the Kiev thingy.
To reassemble the thing, you have to bend the edges of the outer frame over the inner frame again, without damaging the screen. It will work, but i bet not quite, and the screen assembly may well be too wide to drop in the camera again without you pushing hard on it.
But before you reach that stage, you have to make sure the new screen sits at the right depth (and if not, figure out how the get it there - if you know where "there" is), or else focus will be off.
Too much bother. Not worth it. The Kiev screens are no better than the old style Hasselblad screens with split image rangefinder.