score:2
You could try to find a Repair Cafe. There appears to be one in Nรฎmes (https://repaircafe.org/fr/location/repair-cafe-de-nimes), but their website doesn't look entirely up to date.
Upvote:2
You won't find repair shops specialized in strollers and I can't imagine that the employees in a baby/children shop are able to help you on the spot. If you return a defective stroller, they would either replace it or have to return it to the manufacturer for repair. That is not an option if you need a quick fix.
Your easiest option is probably to buy a new stroller. If that is not feasible or too expensive, I can imagine that you might get help in a bicycle repair shop. They will unlikely have special replacement parts for strollers, but if something can be repaired and does not have to be replaced, they may be able to fix whatever is jammed.