Water from melting ice is distributed around the globe, shifting CoG away from Greenland. This new water distribution is therefore uneven, more water getting to the other side.
The land on which you stand may be regarded as a floor. If you put something heavy on a floor, the part near the weight bends down. If you then remove the weight, the floor bends back up (except not 100%). The glacier on Greenland is heavy.
Or perhaps even easier if you include all three. The water that's currently a glacier pushing Greenland down will float elsewhere, and its weight will push most of the world's flooring down, but less so than currently, because the weight of that water will be distributed across a much larger area. That won't compress the planet's magma, ergo, some part of the floor rises as the weight shifts, and the part that lifts is the part under and near Greenland.