Filing case against a carwash due to destroying the engine of a motorcycle

We had our brand new motorcycle for a carwash. It did not start afterward.

We brought it to the showroom shop and they said the water and soap got into the engine and mixed with the oil. In short, the bike is fully destroyed. It is brand new, bought only on September 17.

We went to the carwash. They won't take liability because, to them, they just washed it. Before I file a complaint, I need a lawyer's advice on what to do in this case.