Am I Required To Allow The Repair Shop “fix” Their Mistake Before I Can Sue If They Broke Something Else?

I took my car into a detail shop to have the interior detailed yesterday. After I picked it up and drove away my radio made a loud “pop” and completely went out! I called the detail shop and they were closed. I called first thing this morning and the detail shop said it couldn’t be anything they had done! I took the car to the Honda dealership and they said the radio was fried due to water damage on the interior. I called the detail shop and they refuse to accept responsibility. They keep requesting to be allowed to work on the vehicle themselves in order to determine “if” the radio is in fact broken. What should I do? I don’t want them to break it further!