Need help with incomplete apk app

Hope there is someone that can help me!

I have an incomplete android app that I need to complete.

The company closed down due to covid, but the owner was keen to give me the source code. They send me the APK link to test the app. Changes to the APP was made successfully. The APP consist of 3 APP’s. The 3rd one control the other 2. Basically the APP is finished and need to put on google play store. Is there anyone that can help me. Local company’s want to develop an app from the beginning. or