The phrase "a changing room in" is correct and usable in written English.
It can be used when referring to a specific location or context where a changing room is situated, such as in a building or facility.
Example: "The gym has a changing room in the back for members to use after their workouts."
Alternatives: "a dressing room in" or "a locker room in".
We have a gym and a changing room in the offices so I change quickly and run along the Thames for half an hour.
I'd walk out of a changing room in that case, or ask them to get changed somewhere else... Football is a man's game, and I can't imagine walking into a sauna with a gay after a match". It is, in some ways, sad to see a legendary player become hapless after his career.
Ronnie Corbett enters a changing room in immaculate squash gear and a headband, red of face and covered in sweat.
In mid-September, a small explosive device detonated under a chair in a changing room in a coeducational primary school in Kandahar, causing minor injuries to a teacher.
Yet I am certain that in a changing room in Paris, much less Rome, the narrow little line's authority would be nonexistent, a half-hearted suggestion or maybe just a joke.
I need something nice to wear for the big night, so I am in a changing room in Selfridges trying on a suit that is more expensive than anything I've ever spent money on before, including a house and a trip to Java.
Especially given that it only takes the average human a few seconds in a changing room to figure out whether they would, in fact, be caught dead in those jeans or not.
Of more recent vintage comes a peeling door from a restroom or changing room in Druid Hill Park, uncovered and donated by the City of Baltimore's Department of Recreation and Parks.
Every week during the cricket season I disrobe in a changing room with men of a certain age, and I rue my still decent eyesight.
Ms. Rodriguez's clothes and purse were found in a changing room on the 10th floor, and her cart was found on the eighth floor, the police said.
"I would hate to be in a changing room with lads that didn't believe they could win a game," he said.
