Android App. Advanced changes (i.e. automatic printing on bon-printer when pushupnotification comes etc)

Hi, i have an existing app (done by an indian freelancer called smart1902) for my website [login to view URL] - the app is for the restaurants we are working with, so that they get a notification when there is a new order through our website. i need to make some changes on the app, but i don't have all source code, only the apk file because the other freelancer is on holiday and i can not wait. i know there is an opportunity to unpack the apk file and get the source code and change things. i need following functions: show order notes "neworder" page automatically print on connected bon-printer when the "new order" push up notification shows up. please make me offers about that. thx :)