After some phone calls with the manufacturer “Followit” in Sweden, they advised us to separate the collar from the battery, and leave both components in a warm spot to dry. Since the display notification was still on, it was likely that the data in the collar was safe… But it would have been to time-consuming to send the collar to Sweden, to have it downloaded in the factory. So we had to try to get the data out here. After using some force, we managed to separate the two and leave them to dry.
At least I could do now something and hope!