Help needed, Furby Boom not making high pitch sound

My Furby Boom's motor died, so I sent him to someone who repairs them. I recently got him back, but now he can't make the high pitched sound anymore. Because of that, he can't connect to the app (it worked before and the app recognized him).

His normal voice sounds fine, the only thing he can't make is the high pitched sound. I haven't been able to find any tutorials explaining which part is responsible for making that sound or how to repair it. Any information would be greatly appreciated! 🥺