Help me deploy my back-end app

We were working with some developers that have built us a web app and have handed over all of the code necessary to run the app, however, we are not working with them anymore. We have made some changes to the back-end code (written in PHP) and need to re-deploy the app, which we are unable to do ourselves. In short we need an experienced developer to walk us through how to re-deploy the back-end on Google Cloud Platform.