@Doctor.
Not Sherlock here, but my guess was Sungji removed the towel from Seju and put it back to the bowl because it was falling off from her forehead.
See the panel where Seju called out Sumin.
And Doctor, you are not supposed to leave the towel on the patient's forehead for
too long because as some point temperature will reach equilibrium, and the towel will trap heat instead of extracting heat from the patient.