Behaviour wise, inappetance, struggling to get out of the water or trying to get exposed out of the water.
Conformation wise, eyelids forming, receding gills, receding fins, legs become more muscular, skin texture changes, body shape becomes more 'terrestrial', head shape also becomes more tapered in appearance.
Spontaneous morphs are extremely rare. In most cases, it is poor environmental or nutritional conditions that mimic morphing. These are easily rectified.
If it is indeed a true case of morphing, you would have to change the tank set up to a vivarium suited for terrestrial axies.