In the airlock, Oscar undergoes decontamination. The problem is that at some point the process will be aborted because the level of iodine is insufficient. The automaton is in quarantine.
Since Kate has a particular affinity to the automaton, you will have to load iodine to the airlock - if you don't have any seaweed, run down the stairs and get across the train tracks onto the next platform, take the passage next to the blacksmith's workbench and get one level down. The Seaweed grow near the stairs (left of the stairs, to be exact).
If you already have the seaweed (you could have collected it the previous visit), zoom in on the device that opened asking for iodine. Put some seaweed in and then close it with the mouse. Oscar will soon join Kate - talk to him.
Use the stairs to get to the platform, get across the train tracks, to the blacksmith's. Click on the lighter lying on the table so that Kate lights up the torch.