I bought an app and it had problems, who can help me with that?

Hello friends, I have a question. I purchased an application a while ago, and when I uploaded it to Google Play Console, I had problems with updating the billing library to the latest version. I contacted the owner of the application, but there is no life for whom you are calling. I want your help in updating the billing library and adding advertisements in the application because it is not I have experience in programming the application lab on Android Studio I want your help in this and thank you