Read the thread I posted recently. I just transitioned some to the water. One of them took weeks while the others just a few days.
1.2.0 Cynops Ensicauda Popei new adults adjusting to water help.
You're doing the right thing, just keep them in an aquarium with water that's 1 to 1.5 times high as their length. Put something that floats for them in the beginning but start making it smaller and smaller to force them slowly into the water. Have a lot of plants floating around as well so that they are partially in the water when they're trying to rest on land.
From my understanding, when they are terrestrial, their skin hasn't not adapted the ability to absorb a little bit of oxygen in the water. The only way the acclimate is by getting wet and continuously shedding their skin over and over again and each time they shed their skin in water the better the new skin gets at absorbing water.
My Newts now sleep underwater. I actually haven't seen them use their floating corkbarks I made for them at all for a few weeks now.