Which trade would I call for this (Smell issue)

I received a message from one of my tenants. I am currently abroad so cannot check myself. Usually whenever issues arise I call a plumber, joiner, electrician, etc. For this one I’m unsure who I would call and ask to take a look. It’s a smell issue. Message:

I wanted to bring a concern to your attention regarding my room; for the last couple of days, there’s been a strange odour coming from the wall corner between the room next door and the ____ street-facing corner.

We’ve checked the room, mattress, bed, and floor and are pretty sure it’s coming from the wall or underneath the flooring. (The room next to it seems unaffected.) I think it’s a decaying ammonia smell that’s very hard to describe - quite dense and has a tone of sweetness, not sharp rancid but unpleasant - I’ve tried multiple air fresheners and baking soda and have been leaving the window open most times of the day, which seemed to work at first but it’s getting worse and stronger.

I’m staying in 's room for the moment since it’s difficult and probably not very safe to stay in mine. I’ve checked all the power sockets and they look/smell fine so hopefully it’s not an electrical problem, we’re wondering if something may have gotten into the wall, but I can’t be certain. Could you advise on what steps to take next?

The room is question is not adjascent to the kitchen or bathroom. Who would I call? Any suggestions?

It could be a dead animal, such as a rat. Try pest control.

Ammonia is usually a dead animal / urine

Thanks for the suggestion, I have called a pest control company