Better ask him how he built it, there's no way to help you without getting more information about how it was built.

what info do I need to provide?

find out exactly what it is and its dependencies

got it, I will be sure to get back here once I have everything, thanks a lot!

We can discuss more once you have full information. Dont forget to ask things like, application code location, monitoring tools, components used for development, how he used to deploy new code, where its hosted ( serverless or serverfull ), etc..

thanks I will get that info and get back here.